[Bug 46472] New: Linux kernel 4.19 breaks startup of BO2 due to change in PTRACE_POKEUSER hw breakpoint behavior

[wine-bugs at winehq.org]

https://bugs.winehq.org/show_bug.cgi?id=46472

            Bug ID: 46472
           Summary: Linux kernel 4.19 breaks startup of BO2 due to change
                    in PTRACE_POKEUSER hw breakpoint behavior
           Product: Wine
           Version: 4.0-rc6
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: major
          Priority: P2
         Component: -unknown
          Assignee: wine-bugs at winehq.org
          Reporter: troyb at us.ibm.com
      Distribution: ---

Created attachment 63297
  --> https://bugs.winehq.org/attachment.cgi?id=63297
linux 4.19 commit bd14406b78e6daa1ea3c1673bda1ffc9efdeead0

I bisected Linux 4.18 to 4.19 to find this commit which stops BO2 from
launching under any version of wine from 3.12 to 4.0-rc6, attachment below. 
For convenience I hand-reverted the file kernel/events/hw_breakpoint.c as
follows :

/**
 * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
 * @bp: the breakpoint structure to modify
 * @attr: new breakpoint attributes
 */
int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr
*attr)
{
        int err;

        /*
         * modify_user_hw_breakpoint can be invoked with IRQs disabled and
hence it
         * will not be possible to raise IPIs that invoke __perf_event_disable.
         * So call the function directly after making sure we are targeting the
         * current task.
         */
        if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
                perf_event_disable_local(bp);
        else
                perf_event_disable(bp);

        #if 0
        /* new logic : >= kernel 4.19 */
        err = modify_user_hw_breakpoint_check(bp, attr, false);

        if (!bp->attr.disabled)
                perf_event_enable(bp);

        return err;
        #else
        /* old logic : <kernel 4.19 */
        if (!attr->disabled) {
            err = modify_user_hw_breakpoint_check(bp, attr, false);
            if (err)
               return err;
            perf_event_enable(bp);
            bp->attr.disabled=0;
            }
        return 0;
        #endif
}

I examined some wine source code and found many instance of use of
PTRACE_POKUSER.  I don't know enough about this function to know if this kernel
commit directly breaks the wine code, or some other fault in wine code is
indirectly triggering the problem.  Using "old logic" in the file
hw_breakpoints above enables kernel 4.19 to start BO2 with 4.0-rc6 (and most
likely others).

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