wine-devel April 2024

15 participants
18 discussions

Re: [PATCH v4 00/30] NT synchronization primitive driver

by Elizabeth Figura

On Wednesday, 17 April 2024 05:01:32 CDT Peter Zijlstra wrote: > > > > =================================== > > NT synchronization primitive driver > > =================================== > > > > This page documents the user-space API for the ntsync driver. > > > > ntsync is a support driver for emulation of NT synchronization > > primitives by user-space NT emulators. It exists because implementation > > in user-space, using existing tools, cannot match Windows performance > > while offering accurate semantics. It is implemented entirely in > > software, and does not drive any hardware device. > > > > This interface is meant as a compatibility tool only, and should not > > be used for general synchronization. Instead use generic, versatile > > interfaces such as futex(2) and poll(2). > > > > Synchronization primitives > > ========================== > > > > The ntsync driver exposes three types of synchronization primitives: > > semaphores, mutexes, and events. > > > > A semaphore holds a single volatile 32-bit counter, and a static 32-bit > > integer denoting the maximum value. It is considered signaled when the > > counter is nonzero. The counter is decremented by one when a wait is > > satisfied. Both the initial and maximum count are established when the > > semaphore is created. > > > > A mutex holds a volatile 32-bit recursion count, and a volatile 32-bit > > identifier denoting its owner. A mutex is considered signaled when its > > owner is zero (indicating that it is not owned). The recursion count is > > incremented when a wait is satisfied, and ownership is set to the given > > identifier. > > 'signaled' is used twice now but not defined. For both Semaphore and > Mutex this seems to indicate uncontended? Edit: seems to be needs-wakeup > more than uncontended. Uncontended, yes, or needs-wakeup (I'm not sure what the difference between the two is?) > > A mutex also holds an internal flag denoting whether its previous owner > > has died; such a mutex is said to be abandoned. Owner death is not > > tracked automatically based on thread death, but rather must be > > communicated using NTSYNC_IOC_MUTEX_KILL. An abandoned mutex is > > inherently considered unowned. > > > > Except for the "unowned" semantics of zero, the actual value of the > > owner identifier is not interpreted by the ntsync driver at all. The > > intended use is to store a thread identifier; however, the ntsync > > driver does not actually validate that a calling thread provides > > consistent or unique identifiers. > > Why not verify it? Seems simple enough to put in a TID check, esp. if NT > mandates the same. I mostly figured it'd be simplest to leave the driver completely agnostic, but I don't think there's any reason we can't use the real TID for most calls. > > An event holds a volatile boolean state denoting whether it is signaled > > or not. There are two types of events, auto-reset and manual-reset. An > > auto-reset event is designaled when a wait is satisfied; a manual-reset > > event is not. The event type is specified when the event is created. > > But what is an event? I'm familiar with semaphores and mutexes, but less > so with events. It's what I'm trying to define there, a single bit of state that's either contended or not. It acts broadly like an eventfd, in that you can wake (write) or wait (read), but without the distinction of having different nonzero values in the internal counter. You could also think of it as a semaphore with a maximum count of one. However, unlike a semaphore it also supports the "pulse" operation, and you can also have "manual-reset" events that *don't* change state when you wait on them (no equivalent for regular semaphores). > > Unless specified otherwise, all operations on an object are atomic and > > totally ordered with respect to other operations on the same object. > > > > Objects are represented by files. When all file descriptors to an > > object are closed, that object is deleted. > > > > Char device > > =========== > > > > The ntsync driver creates a single char device /dev/ntsync. Each file > > description opened on the device represents a unique instance intended > > to back an individual NT virtual machine. Objects created by one ntsync > > instance may only be used with other objects created by the same > > instance. > > > > ioctl reference > > =============== > > > > All operations on the device are done through ioctls. There are four > > structures used in ioctl calls:: > > > > struct ntsync_sem_args { > > __u32 sem; > > __u32 count; > > __u32 max; > > }; > > > > struct ntsync_mutex_args { > > __u32 mutex; > > __u32 owner; > > __u32 count; > > }; > > > > struct ntsync_event_args { > > __u32 event; > > __u32 signaled; > > __u32 manual; > > }; > > > > struct ntsync_wait_args { > > __u64 timeout; > > __u64 objs; > > __u32 count; > > __u32 owner; > > __u32 index; > > __u32 alert; > > __u32 flags; > > __u32 pad; > > }; > > > > Depending on the ioctl, members of the structure may be used as input, > > output, or not at all. All ioctls return 0 on success. > > > > The ioctls on the device file are as follows: > > > > NTSYNC_IOC_CREATE_SEM > > > > Create a semaphore object. Takes a pointer to struct ntsync_sem_args, > > which is used as follows: > > > > * sem: On output, contains a file descriptor to the created semaphore. > > * count: Initial count of the semaphore. > > * max: Maximum count of the semaphore. > > > > Fails with EINVAL if `count` is greater than `max`. > > So the implication is that @count and @max are input argument and as > such should be set before calling the ioctl()? > > It would not have been weird to have the ioctl() return the fd on > success I suppose, instead of mixing input and output arguments like > this, but whatever, this works. I think that would have been fine, and I could still change it accordingly. The reason I didn't do that was that [1] advises against it (although I don't know why). [1] https://docs.kernel.org/driver-api/ioctl.html#return-code > > The ioctls on the individual objects are as follows: > > > > NTSYNC_IOC_SEM_POST > > > > Post to a semaphore object. Takes a pointer to a 32-bit integer, > > which on input holds the count to be added to the semaphore, and on > > output contains its previous count. > > > > If adding to the semaphore's current count would raise the latter > > past the semaphore's maximum count, the ioctl fails with > > EOVERFLOW and the semaphore is not affected. If raising the > > semaphore's count causes it to become signaled, eligible threads > > waiting on this semaphore will be woken and the semaphore's count > > decremented appropriately. > > Urg, so this is the traditional V (vrijgeven per Dijkstra, release in > English), but now 'conveniently' called POST, such that it can be > readily confused with the P operation (passering, or passing) which it > is not. > > Glorious :-/ > > You're of course going to tell me NT did this and you can't help this > naming foible. No, NT calls it "release" (and the operation on a mutex is also "release" rather than "unlock".) I called it "post" after POSIX semaphores, on the idea that it'd be more familiar to a Unix developer (and shorter). I see I was wrong, so I'll rename it to "release". > > NTSYNC_IOC_MUTEX_UNLOCK > > > > Release a mutex object. Takes a pointer to struct ntsync_mutex_args, > > which is used as follows: > > > > * mutex: Ignored. > > * owner: Specifies the owner trying to release this mutex. > > * count: On output, contains the previous recursion count. > > > > If "owner" is zero, the ioctl fails with EINVAL. If "owner" > > is not the current owner of the mutex, the ioctl fails with > > EPERM. > > ISTR you having written elsewhere that NT actually demands mutexes to be > strictly per thread, which for the above would mandate @owner to be > current, no? Right. We could replace owner with current everywhere except for NTSYNC_IOC_KILL_OWNER. > > The mutex's count will be decremented by one. If decrementing the > > mutex's count causes it to become zero, the mutex is marked as > > unowned and signaled, and eligible threads waiting on it will be > > woken as appropriate. > > > > NTSYNC_IOC_SET_EVENT > > > > Signal an event object. Takes a pointer to a 32-bit integer, which on > > output contains the previous state of the event. > > > > Eligible threads will be woken, and auto-reset events will be > > designaled appropriately. > > Hmm, so the event thing is like a simple wait-wake scheme? Where the > 'signaled' bit is used as the wakeup state? Yes, exactly. > > NTSYNC_IOC_RESET_EVENT > > > > Designal an event object. Takes a pointer to a 32-bit integer, which > > on output contains the previous state of the event. > > > > NTSYNC_IOC_PULSE_EVENT > > > > Wake threads waiting on an event object while leaving it in an > > unsignaled state. Takes a pointer to a 32-bit integer, which on > > output contains the previous state of the event. > > > > A pulse operation can be thought of as a set followed by a reset, > > performed as a single atomic operation. If two threads are waiting on > > an auto-reset event which is pulsed, only one will be woken. If two > > threads are waiting a manual-reset event which is pulsed, both will > > be woken. However, in both cases, the event will be unsignaled > > afterwards, and a simultaneous read operation will always report the > > event as unsignaled. > > *groan* Yep :D This one is terrible, and it's the only one that Microsoft has come out and explicitly said "don't use this". Supposedly their kernel is even coded such that if a waiting thread gets hit by an interrupt that the pulse will go unnoticed, although I've tried to reproduce this in practice and been unsuccessful. But of course it's terrible regardless, because you never know if your thread is waiting or not. In practice it seems to usually be used on a timer, though, so that part doesn't matter as much. > > NTSYNC_IOC_READ_SEM > > > > Read the current state of a semaphore object. Takes a pointer to > > struct ntsync_sem_args, which is used as follows: > > > > * sem: Ignored. > > * count: On output, contains the current count of the semaphore. > > * max: On output, contains the maximum count of the semaphore. > > This seems inherently racy -- what is the intended purpose of this > interface? > > Specifically the moment a value is returned, either P or V operations > can change it, rendering the (as yet unused) return value incorrect. I have no idea what it's intended for. Actually it's not even exposed as a documented API, only an undocumented one. But it does work, and applications use it. > > NTSYNC_IOC_READ_MUTEX > > > > Read the current state of a mutex object. Takes a pointer to struct > > ntsync_mutex_args, which is used as follows: > > > > * mutex: Ignored. > > * owner: On output, contains the current owner of the mutex, or zero > > if the mutex is not currently owned. > > * count: On output, contains the current recursion count of the mutex. > > > > If the mutex is marked as abandoned, the function fails with > > EOWNERDEAD. In this case, "count" and "owner" are set to zero. > > Another questionable interface. I suspect you're going to be telling me > NT has them so you have to have them, but urgh. Unfortunately yes. > > NTSYNC_IOC_READ_EVENT > > > > Read the current state of an event object. Takes a pointer to struct > > ntsync_event_args, which is used as follows: > > > > * event: Ignored. > > * signaled: On output, contains the current state of the event. > > * manual: On output, contains 1 if the event is a manual-reset event, > > and 0 otherwise. > > I can't help but notice all those @sem, @mutex, @event 'output' members > being unused except for create. Seems like a waste to have them. Yes, mostly so I could reuse the existing structures. On the other hand if there's no reason not to return fds from the create ioctls, then we could just remove those members. > > NTSYNC_IOC_KILL_OWNER > > > > Mark a mutex as unowned and abandoned if it is owned by the given > > owner. Takes an input-only pointer to a 32-bit integer denoting the > > owner. If the owner is zero, the ioctl fails with EINVAL. If the > > owner does not own the mutex, the function fails with EPERM. > > > > Eligible threads waiting on the mutex will be woken as appropriate > > (and such waits will fail with EOWNERDEAD, as described below). > > Wine will use this when it detects a thread exit I suppose. Exactly. > > NTSYNC_IOC_WAIT_ANY > > > > Poll on any of a list of objects, atomically acquiring at most one. > > Takes a pointer to struct ntsync_wait_args, which is used as follows: > > > > * timeout: Absolute timeout in nanoseconds. If NTSYNC_WAIT_REALTIME > > is set, the timeout is measured against the REALTIME > > clock; otherwise it is measured against the MONOTONIC > > clock. If the timeout is equal to or earlier than the > > current time, the function returns immediately without > > sleeping. If "timeout" is U64_MAX, the function will > > sleep until an object is signaled, and will not fail > > with ETIMEDOUT. > > > > * objs: Pointer to an array of "count" file descriptors > > (specified as an integer so that the structure has the > > same size regardless of architecture). If any object is > > invalid, the function fails with EINVAL. > > > > * count: Number of objects specified in the "objs" array. If > > greater than NTSYNC_MAX_WAIT_COUNT, the function fails > > with EINVAL. > > > > * owner: Mutex owner identifier. If any object in "objs" is a > > mutex, the ioctl will attempt to acquire that mutex on > > behalf of "owner". If "owner" is zero, the ioctl > > fails with EINVAL. > > Again, should that not be current? That is, why not maintain the NT > invariant and mandates TIDs and avoid the arguments in both cases? I don't think there's any particular reason. > > * index: On success, contains the index (into "objs") of the > > object which was signaled. If "alert" was signaled > > instead, this contains "count". > > Could be the actual return value, no? Edit: no it cannot be because > -EOWNERDEAD case below. Yeah. Again the advice about "only return zero from an ioctl", too. Although we could also use a bit in the return value (which is also kind of what NT does). > > A semaphore is considered to be signaled if its count is nonzero, and > > is acquired by decrementing its count by one. A mutex is considered > > to be signaled if it is unowned or if its owner matches the "owner" > > argument, and is acquired by incrementing its recursion count by one > > and setting its owner to the "owner" argument. An auto-reset event > > is acquired by designaling it; a manual-reset event is not affected > > by acquisition. > > > > Acquisition is atomic and totally ordered with respect to other > > operations on the same object. If two wait operations (with different > > "owner" identifiers) are queued on the same mutex, only one is > > signaled. If two wait operations are queued on the same semaphore, > > and a value of one is posted to it, only one is signaled. The order > > in which threads are signaled is not specified. > > Note that you do list the lack of guarantee here, but not above. I > suspect both cases are similar and guarantee nothing. There's no documented guarantee in either case, but when testing in controlled well-ordered environments, NtWaitForMultipleObjects() always acquires the lowest index first, and I think wakes are FIFO. I'm not really sure why I specified the guarantee for the former but not the latter. > > The "alert" argument is an "extra" event which can terminate the > > wait, independently of all other objects. If members of "objs" and > > "alert" are both simultaneously signaled, a member of "objs" will > > always be given priority and acquired first. > > > > It is valid to pass the same object more than once, including by > > passing the same event in the "objs" array and in "alert". If a > > wakeup occurs due to that object being signaled, "index" is set to > > the lowest index corresponding to that object. > > Urgh, is this an actual guarantee? This almost seems to imply that at > [A] above we can indeed guarantee the lowest indexed object is acquired > first. It's definitely legal in NT to pass the same object more than once (in wait-for-any, not wait-for-all though), and it's definitely the case that (at least in controlled well-ordered environments) the lowest index is acquired first. I don't know of any application that definitely depends on either of these, and they're not documented behaviours, but Wine has implemented those behaviours and it would make me nervous to break them here. The part about passing the same event in "alert" and "objs" is not part of NT exactly (in NT the "alert" isn't even an event; it's a special bit of thread state; we just use an event for simplicity). I think I specified it just to avoid coding an extra check (since it should Just Work), while also making it clear that case was considered. > > The function may fail with EINTR if a signal is received. > > In which case @index must be disregarded since nothing will be acquired, > right? > > So far nothing really weird, and I'm thinking futexes should be able to > do all this, no? Even disregarding wait-for-all, futexes aren't really good enough. Wait operations need to consume state, and while we could put that state in user space (and in fact we *do* have an out of tree patch set that kind of does this) that requires all that state to be shared across processes, which is a problem since we want processes to be isolated unless they explicitly share objects with each other. There's not a scalable way to achieve this, especially since you can share objects lazily. You also cannot do NtPulseEvent() this way. The aforementioned patch set badly emulates it and it does in practice break any application that uses it. Similarly there are some applications that do a weird "fake pulse" where they set and then immediately reset an event from the same thread, and expect that to always wake.

2 weeks, 3 days

Re: [PATCH v4 00/30] NT synchronization primitive driver

by Elizabeth Figura

On Friday, 19 April 2024 11:16:11 CDT Peter Zijlstra wrote: > On Tue, Apr 16, 2024 at 05:18:56PM -0500, Elizabeth Figura wrote: > > On Tuesday, 16 April 2024 16:18:24 CDT Elizabeth Figura wrote: > > > On Tuesday, 16 April 2024 03:14:21 CDT Peter Zijlstra wrote: > > > > I don't support GE has it in his builds? Last time I tried, building > > > > Wine was a bit of a pain. > > > > > > It doesn't seem so. I tried to build a GE-compatible ntsync build, uploaded > > > here (thanks Arek for hosting): > > > > > > https://f002.backblazeb2.com/file/wine-ntsync/ntsync-wine.tar.xz > > > > Oops, the initial version I uploaded had broken paths. Should be fixed now. > > > > (It's also broken on an unpatched kernel unless explicitly disabled with > > WINE_DISABLE_FAST_SYNC=1. Not sure what I messed up there—it should fall back > > cleanly—but hopefully shouldn't be too important for testing.) > > So I've tried using that wine build with lutris, and I can't get it to > start EGS or anything else. > > I even added a printk to the ntsync driver for every open, to see if it > gets that far, but I'm not even getting that :/ That's odd, it works for me, both as a standalone build and with lutris... Does /dev/ntsync exist (module is loaded) and have nonzero permissions? I forgot to mention that's necessary, sorry. Otherwise I can try to look at an strace, or a Wine debug log. I don't think there's an easy way to get the latter with Lutris, but something like `WINEDEBUG=+all ./wine winecfg 2>log` should work.

3 weeks, 5 days

Re: Alexandre Julliard : dbghelp: Ignore a couple of Dwarf-3 opcodes.

by Eric Pouech

Le 29/04/2024 à 22:22, Alexandre Julliard a écrit : > Module: wine > Branch: master > Commit: 754f11a4adc2b7431837a92448b93bb845d99d61 > URL: https://gitlab.winehq.org/wine/wine/-/commit/754f11a4adc2b7431837a92448b93b… > > Author: Alexandre Julliard <julliard(a)winehq.org> > Date: Sun Apr 28 16:06:54 2024 +0200 > > dbghelp: Ignore a couple of Dwarf-3 opcodes. Hi for curiosity, how did you get these ? (clang ?) (for the record, dbghelp doesn't generate yet prologue & epilogue tagging in dwarf debug info (it's done for pdb)) A+

1 month

Re: Fwd: Bumping the minimum supported macOS version

by Tim Clem

I would prefer 10.15 in particular so we could drop support for native (i.e. macho) 32-bit binaries. That would allow us to use modern Obj-C runtime features (e.g. auto-synthesis) and eventually consider ARC. It's also worth noting that winehq's gitlab CI runs 10.15. On 4/11/24 11:06 AM, dgreer(a)codeweavers.com wrote: > I can safely say that upstream wine hasn't work on 10.8 since 7.22 ish, > wine-8.21 the lowest is probably 10.10 though I've aired on the side of > caution and locked 7.22 to require 10.11. > > The absolute lowest would be 10.13 though I'd already dropped support > below 10.15 in the winehq packages (installed via brew cask system), > myself and Marzent have long been in favor of upping the minimum > requirement for sometime. > > ---------- Forwarded message --------- > From: *Tim Clem* <tclem(a)codeweavers.com <mailto:[email protected]>> > Date: Thu, Apr 11, 2024 at 1:51 PM > Subject: Bumping the minimum supported macOS version > To: <wine-devel(a)winehq.org <mailto:[email protected]>> > > > Hello everyone-- > > I'm proposing raising the official minimum supported macOS version to > Catalina, 10.15. According to the wiki > (https://wiki.winehq.org/MacOS <https://wiki.winehq.org/MacOS>), we > theoretically support 10.8. > > Does anyone object? > > Thanks! > --Tim > > >

1 month

Bugzilla having issues sending mail

by Austin English

An unexpected error occurred. This could be a temporary problem, or some code is behaving incorrectly. If this problem persists, please email this page to wine-bugs(a)winehq.org with details of what you were doing at the time this message appeared. URL: https://bugs.winehq.org/process_bug.cgi There was an error sending mail from '"WineHQ Bugzilla" <wine-bugs(a)winehq.org>' to 'dark.shadow4(a)web.de': Couldn't connect to mail.winehq.org Traceback: at Bugzilla/Mailer.pm line 162. Bugzilla::Mailer::MessageToMTA(...) called at Bugzilla/BugMail.pm line 354 Bugzilla::BugMail::sendMail(...) called at Bugzilla/BugMail.pm line 255 Bugzilla::BugMail::Send(...) called at Bugzilla/Bug.pm line 1200 Bugzilla::Bug::_send_bugmail(...) called at Bugzilla/Bug.pm line 1138 Bugzilla::Bug::send_changes(...) called at /home/winehq/opt/bugzilla/process_bug.cgi line 378 -- -Austin GPG: 267B CC1F 053F 0749 (expires 2026-03-03)

1 month

Upcoming vkd3d 1.12 release

by Henri Verbeet

Hi all, The planned release date for vkd3d 1.12 is May 28. The development branch will become increasingly frozen as we're nearing that date, starting with a freeze of the public API after April 30. Features will be frozen after May 14. If you're an upstream vkd3d developer, please do the following: - Keep an eye on Bugzilla for any reported regressions. - Review any API changes since the previous release. - Verify all the vkd3d tests pass on your hardware, and please send fixes if they don't. - Review and improve the documentation. - Apply your best judgment about which patches are appropriate for the current stage of the release process. If you're a downstream user of vkd3d, please test your applications for regressions, and file bug reports if you find any. If you're the maintainer of a Wine module that (indirectly) depends on vkd3d, like e.g. d2d1, d3dx9, d3dcompiler, or any of the core Direct3D modules, that includes making sure the unit tests still pass with the new version. The planned release date for vkd3d 1.13 is August 29. Regards, Henri

1 month, 1 week

Wine staging 9.7 release

by Alistair Leslie-Hughes

Binary packages for various distributions will be available from: https://www.winehq.org/download Summary since last release * Rebased to current wine 9.7 (432 patches are applied to wine vanilla) Upstreamed (Either directly from staging or fixed with a similar patch). * widl: Add support for recursive type references to SLTG typelib generator. * widl: Add support for interfaces to SLTG typelib generator. * widl: Add support for inherited interfaces to SLTG typelib generator. * ntdll: Add fake data implementation for ProcessQuotaLimits class. Removed (No longer required). * None Added: * None. Updated: * vkd3d-latest * kernel32-CopyFileEx NOTE: The updated ntdll-WRITECOPY patchset now allow Battle.net to run. Where can you help * Run Steam/Battle.net/GOG/UPlay/Epic * Test your favorite game. * Test your favorite applications. * Improve staging patches and get them accepted upstream. * Suggest patches to be included in staging. As always, if you find a bug, please report it via https://bugs.winehq.org Best Regards Alistair.

1 month, 1 week

Mailing list traffic

by Francois Gouget

With GitLab and the spinning off of commit messages to wine-gitlab I think the traffic estimates on the mailing list page need to be updated... at least for wine-devel: it no longer has 50 messages per day. https://www.winehq.org/forums (unfortunately there is no unit on the little per mailing-list graph) -- Francois Gouget <fgouget(a)free.fr> http://fgouget.free.fr/ Theory is where you know everything but nothing works. Practice is where everything works but nobody knows why. Sometimes they go hand in hand: nothing works and nobody knows why.

1 month, 1 week

Re: [PATCH v4 02/27] ntsync: Introduce NTSYNC_IOC_WAIT_ALL.

by Elizabeth Figura

On Wednesday, 17 April 2024 06:37:03 CDT Peter Zijlstra wrote: > On Mon, Apr 15, 2024 at 08:08:12PM -0500, Elizabeth Figura wrote: > > + if (atomic_read(&sem->all_hint) > 0) { > > + spin_lock(&dev->wait_all_lock); > > + spin_lock_nest_lock(&sem->lock, &dev->wait_all_lock); > > > > + prev_count = sem->u.sem.count; > > + ret = post_sem_state(sem, args); > > + if (!ret) { > > + try_wake_all_obj(dev, sem); > > + try_wake_any_sem(sem); > > + } > > > > + spin_unlock(&sem->lock); > > + spin_unlock(&dev->wait_all_lock); > > + } else { > > + spin_lock(&sem->lock); > > + > > + prev_count = sem->u.sem.count; > > + ret = post_sem_state(sem, args); > > + if (!ret) > > + try_wake_any_sem(sem); > > + > > + spin_unlock(&sem->lock); > > + } > > > > if (!ret && put_user(prev_count, user_args)) > > ret = -EFAULT; > > vs. > > > + /* queue ourselves */ > > + > > + spin_lock(&dev->wait_all_lock); > > + > > + for (i = 0; i < args.count; i++) { > > + struct ntsync_q_entry *entry = &q->entries[i]; > > + struct ntsync_obj *obj = entry->obj; > > + > > + atomic_inc(&obj->all_hint); > > + > > + /* > > + * obj->all_waiters is protected by dev->wait_all_lock rather > > + * than obj->lock, so there is no need to acquire obj->lock > > + * here. > > + */ > > + list_add_tail(&entry->node, &obj->all_waiters); > > + } > > This looks racy, consider: > > atomic_read(all_hints) /* 0 */ > > spin_lock(wait_all_lock) > atomic_inc(all_hint) /* 1 */ > list_add_tail() > > spin_lock(sem->lock) > /* try_wake_all_obj() missing */ > > > > > I've not yet thought about if this is harmful or not, but if not, it > definitely needs a comment. > > Anyway, I need a break, maybe more this evening. Ach. I wrote this with the idea that the race isn't meaningful, but looking at it again you're right—there is a harmful race here. I think it should be fixable by moving the atomic_read inside the lock, though.

1 month, 2 weeks

Re: [PATCH v4 00/30] NT synchronization primitive driver

by Elizabeth Figura

On Wednesday, 17 April 2024 00:22:18 CDT Peter Zijlstra wrote: > On Tue, Apr 16, 2024 at 04:18:19PM -0500, Elizabeth Figura wrote: > > Let me know if that's good enough or if I should try to render it into > > plain text somehow. > > Plain text is much preferred. I'm more of a text editor kinda guy -- > being a programmer and all that. I can certainly sympathize with that ;-) Here's a (slightly ad-hoc) simplification of the patch into text form inlined into this message; hopefully it's readable enough. =================================== NT synchronization primitive driver =================================== This page documents the user-space API for the ntsync driver. ntsync is a support driver for emulation of NT synchronization primitives by user-space NT emulators. It exists because implementation in user-space, using existing tools, cannot match Windows performance while offering accurate semantics. It is implemented entirely in software, and does not drive any hardware device. This interface is meant as a compatibility tool only, and should not be used for general synchronization. Instead use generic, versatile interfaces such as futex(2) and poll(2). Synchronization primitives ========================== The ntsync driver exposes three types of synchronization primitives: semaphores, mutexes, and events. A semaphore holds a single volatile 32-bit counter, and a static 32-bit integer denoting the maximum value. It is considered signaled when the counter is nonzero. The counter is decremented by one when a wait is satisfied. Both the initial and maximum count are established when the semaphore is created. A mutex holds a volatile 32-bit recursion count, and a volatile 32-bit identifier denoting its owner. A mutex is considered signaled when its owner is zero (indicating that it is not owned). The recursion count is incremented when a wait is satisfied, and ownership is set to the given identifier. A mutex also holds an internal flag denoting whether its previous owner has died; such a mutex is said to be abandoned. Owner death is not tracked automatically based on thread death, but rather must be communicated using NTSYNC_IOC_MUTEX_KILL. An abandoned mutex is inherently considered unowned. Except for the "unowned" semantics of zero, the actual value of the owner identifier is not interpreted by the ntsync driver at all. The intended use is to store a thread identifier; however, the ntsync driver does not actually validate that a calling thread provides consistent or unique identifiers. An event holds a volatile boolean state denoting whether it is signaled or not. There are two types of events, auto-reset and manual-reset. An auto-reset event is designaled when a wait is satisfied; a manual-reset event is not. The event type is specified when the event is created. Unless specified otherwise, all operations on an object are atomic and totally ordered with respect to other operations on the same object. Objects are represented by files. When all file descriptors to an object are closed, that object is deleted. Char device =========== The ntsync driver creates a single char device /dev/ntsync. Each file description opened on the device represents a unique instance intended to back an individual NT virtual machine. Objects created by one ntsync instance may only be used with other objects created by the same instance. ioctl reference =============== All operations on the device are done through ioctls. There are four structures used in ioctl calls:: struct ntsync_sem_args { __u32 sem; __u32 count; __u32 max; }; struct ntsync_mutex_args { __u32 mutex; __u32 owner; __u32 count; }; struct ntsync_event_args { __u32 event; __u32 signaled; __u32 manual; }; struct ntsync_wait_args { __u64 timeout; __u64 objs; __u32 count; __u32 owner; __u32 index; __u32 alert; __u32 flags; __u32 pad; }; Depending on the ioctl, members of the structure may be used as input, output, or not at all. All ioctls return 0 on success. The ioctls on the device file are as follows: .. NTSYNC_IOC_CREATE_SEM Create a semaphore object. Takes a pointer to struct ntsync_sem_args, which is used as follows: * sem: On output, contains a file descriptor to the created semaphore. * count: Initial count of the semaphore. * max: Maximum count of the semaphore. Fails with EINVAL if `count` is greater than `max`. .. NTSYNC_IOC_CREATE_MUTEX Create a mutex object. Takes a pointer to struct ntsync_mutex_args, which is used as follows: * mutex: On output, contains a file descriptor to the created mutex. * count: Initial recursion count of the mutex. * owner: Initial owner of the mutex. If ``owner`` is nonzero and ``count`` is zero, or if ``owner`` is zero and ``count`` is nonzero, the function fails with EINVAL. .. NTSYNC_IOC_CREATE_EVENT Create an event object. Takes a pointer to struct ntsync_event_args, which is used as follows: * event: On output, contains a file descriptor to the created event. * signaled: If nonzero, the event is initially signaled, otherwise nonsignaled. * manual: If nonzero, the event is a manual-reset event, otherwise auto-reset. The ioctls on the individual objects are as follows: .. NTSYNC_IOC_SEM_POST Post to a semaphore object. Takes a pointer to a 32-bit integer, which on input holds the count to be added to the semaphore, and on output contains its previous count. If adding to the semaphore's current count would raise the latter past the semaphore's maximum count, the ioctl fails with EOVERFLOW and the semaphore is not affected. If raising the semaphore's count causes it to become signaled, eligible threads waiting on this semaphore will be woken and the semaphore's count decremented appropriately. .. NTSYNC_IOC_MUTEX_UNLOCK Release a mutex object. Takes a pointer to struct ntsync_mutex_args, which is used as follows: * mutex: Ignored. * owner: Specifies the owner trying to release this mutex. * count: On output, contains the previous recursion count. If ``owner`` is zero, the ioctl fails with EINVAL. If ``owner`` is not the current owner of the mutex, the ioctl fails with EPERM. The mutex's count will be decremented by one. If decrementing the mutex's count causes it to become zero, the mutex is marked as unowned and signaled, and eligible threads waiting on it will be woken as appropriate. .. NTSYNC_IOC_SET_EVENT Signal an event object. Takes a pointer to a 32-bit integer, which on output contains the previous state of the event. Eligible threads will be woken, and auto-reset events will be designaled appropriately. .. NTSYNC_IOC_RESET_EVENT Designal an event object. Takes a pointer to a 32-bit integer, which on output contains the previous state of the event. .. NTSYNC_IOC_PULSE_EVENT Wake threads waiting on an event object while leaving it in an unsignaled state. Takes a pointer to a 32-bit integer, which on output contains the previous state of the event. A pulse operation can be thought of as a set followed by a reset, performed as a single atomic operation. If two threads are waiting on an auto-reset event which is pulsed, only one will be woken. If two threads are waiting a manual-reset event which is pulsed, both will be woken. However, in both cases, the event will be unsignaled afterwards, and a simultaneous read operation will always report the event as unsignaled. .. NTSYNC_IOC_READ_SEM Read the current state of a semaphore object. Takes a pointer to struct ntsync_sem_args, which is used as follows: * sem: Ignored. * count: On output, contains the current count of the semaphore. * max: On output, contains the maximum count of the semaphore. .. NTSYNC_IOC_READ_MUTEX Read the current state of a mutex object. Takes a pointer to struct ntsync_mutex_args, which is used as follows: * mutex: Ignored. * owner: On output, contains the current owner of the mutex, or zero if the mutex is not currently owned. * count: On output, contains the current recursion count of the mutex. If the mutex is marked as abandoned, the function fails with EOWNERDEAD. In this case, ``count`` and ``owner`` are set to zero. .. NTSYNC_IOC_READ_EVENT Read the current state of an event object. Takes a pointer to struct ntsync_event_args, which is used as follows: * event: Ignored. * signaled: On output, contains the current state of the event. * manual: On output, contains 1 if the event is a manual-reset event, and 0 otherwise. .. NTSYNC_IOC_KILL_OWNER Mark a mutex as unowned and abandoned if it is owned by the given owner. Takes an input-only pointer to a 32-bit integer denoting the owner. If the owner is zero, the ioctl fails with EINVAL. If the owner does not own the mutex, the function fails with EPERM. Eligible threads waiting on the mutex will be woken as appropriate (and such waits will fail with EOWNERDEAD, as described below). .. NTSYNC_IOC_WAIT_ANY Poll on any of a list of objects, atomically acquiring at most one. Takes a pointer to struct ntsync_wait_args, which is used as follows: * timeout: Absolute timeout in nanoseconds. If NTSYNC_WAIT_REALTIME is set, the timeout is measured against the REALTIME clock; otherwise it is measured against the MONOTONIC clock. If the timeout is equal to or earlier than the current time, the function returns immediately without sleeping. If ``timeout`` is U64_MAX, the function will sleep until an object is signaled, and will not fail with ETIMEDOUT. * objs: Pointer to an array of ``count`` file descriptors (specified as an integer so that the structure has the same size regardless of architecture). If any object is invalid, the function fails with EINVAL. * count: Number of objects specified in the ``objs`` array. If greater than NTSYNC_MAX_WAIT_COUNT, the function fails with EINVAL. * owner: Mutex owner identifier. If any object in ``objs`` is a mutex, the ioctl will attempt to acquire that mutex on behalf of ``owner``. If ``owner`` is zero, the ioctl fails with EINVAL. * index: On success, contains the index (into ``objs``) of the object which was signaled. If ``alert`` was signaled instead, this contains ``count``. * alert: Optional event object file descriptor. If nonzero, this specifies an "alert" event object which, if signaled, will terminate the wait. If nonzero, the identifier must point to a valid event. * flags: Zero or more flags. Currently the only flag is NTSYNC_WAIT_REALTIME, which causes the timeout to be measured against the REALTIME clock instead of MONOTONIC. * pad: Unused, must be set to zero. This function attempts to acquire one of the given objects. If unable to do so, it sleeps until an object becomes signaled, subsequently acquiring it, or the timeout expires. In the latter case the ioctl fails with ETIMEDOUT. The function only acquires one object, even if multiple objects are signaled. A semaphore is considered to be signaled if its count is nonzero, and is acquired by decrementing its count by one. A mutex is considered to be signaled if it is unowned or if its owner matches the ``owner`` argument, and is acquired by incrementing its recursion count by one and setting its owner to the ``owner`` argument. An auto-reset event is acquired by designaling it; a manual-reset event is not affected by acquisition. Acquisition is atomic and totally ordered with respect to other operations on the same object. If two wait operations (with different ``owner`` identifiers) are queued on the same mutex, only one is signaled. If two wait operations are queued on the same semaphore, and a value of one is posted to it, only one is signaled. The order in which threads are signaled is not specified. If an abandoned mutex is acquired, the ioctl fails with EOWNERDEAD. Although this is a failure return, the function may otherwise be considered successful. The mutex is marked as owned by the given owner (with a recursion count of 1) and as no longer abandoned, and ``index`` is still set to the index of the mutex. The ``alert`` argument is an "extra" event which can terminate the wait, independently of all other objects. If members of ``objs`` and ``alert`` are both simultaneously signaled, a member of ``objs`` will always be given priority and acquired first. It is valid to pass the same object more than once, including by passing the same event in the ``objs`` array and in ``alert``. If a wakeup occurs due to that object being signaled, ``index`` is set to the lowest index corresponding to that object. The function may fail with EINTR if a signal is received. .. NTSYNC_IOC_WAIT_ALL Poll on a list of objects, atomically acquiring all of them. Takes a pointer to struct ntsync_wait_args, which is used identically to NTSYNC_IOC_WAIT_ANY, except that ``index`` is always filled with zero on success if not woken via alert. This function attempts to simultaneously acquire all of the given objects. If unable to do so, it sleeps until all objects become simultaneously signaled, subsequently acquiring them, or the timeout expires. In the latter case the ioctl fails with ETIMEDOUT and no objects are modified. Objects may become signaled and subsequently designaled (through acquisition by other threads) while this thread is sleeping. Only once all objects are simultaneously signaled does the ioctl acquire them and return. The entire acquisition is atomic and totally ordered with respect to other operations on any of the given objects. If an abandoned mutex is acquired, the ioctl fails with EOWNERDEAD. Similarly to NTSYNC_IOC_WAIT_ANY, all objects are nevertheless marked as acquired. Note that if multiple mutex objects are specified, there is no way to know which were marked as abandoned. As with "any" waits, the ``alert`` argument is an "extra" event which can terminate the wait. Critically, however, an "all" wait will succeed if all members in ``objs`` are signaled, *or* if ``alert`` is signaled. In the latter case ``index`` will be set to ``count``. As with "any" waits, if both conditions are filled, the former takes priority, and objects in ``objs`` will be acquired. Unlike NTSYNC_IOC_WAIT_ANY, it is not valid to pass the same object more than once, nor is it valid to pass the same object in ``objs`` and in ``alert``. If this is attempted, the function fails with EINVAL.

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wine-devel April 2024