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| author | Akihiko Odaki <akihiko.odaki@daynix.com> | 2025-05-29 14:45:50 +0900 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2025-06-06 14:32:55 +0200 |
| commit | 6e2d11bf04fb18e60afc8551871d9acb7b56983d (patch) | |
| tree | 744dbbcb8debe3ef51de012bef56c1e732ab3481 /include/qemu | |
| parent | 4cdc489eb9c25f76255a550a4a0b19cda3435a76 (diff) | |
| download | focaccia-qemu-6e2d11bf04fb18e60afc8551871d9acb7b56983d.tar.gz focaccia-qemu-6e2d11bf04fb18e60afc8551871d9acb7b56983d.zip | |
futex: Check value after qemu_futex_wait()
futex(2) - Linux manual page https://man7.org/linux/man-pages/man2/futex.2.html > Note that a wake-up can also be caused by common futex usage patterns > in unrelated code that happened to have previously used the futex > word's memory location (e.g., typical futex-based implementations of > Pthreads mutexes can cause this under some conditions). Therefore, > callers should always conservatively assume that a return value of 0 > can mean a spurious wake-up, and use the futex word's value (i.e., > the user-space synchronization scheme) to decide whether to continue > to block or not. Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com> Link: https://lore.kernel.org/r/20250529-event-v5-1-53b285203794@daynix.com Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'include/qemu')
| -rw-r--r-- | include/qemu/futex.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/include/qemu/futex.h b/include/qemu/futex.h index 91ae88966e..f577740053 100644 --- a/include/qemu/futex.h +++ b/include/qemu/futex.h @@ -24,6 +24,15 @@ static inline void qemu_futex_wake(void *f, int n) qemu_futex(f, FUTEX_WAKE, n, NULL, NULL, 0); } +/* + * Note that a wake-up can also be caused by common futex usage patterns in + * unrelated code that happened to have previously used the futex word's + * memory location (e.g., typical futex-based implementations of Pthreads + * mutexes can cause this under some conditions). Therefore, callers should + * always conservatively assume that it is a spurious wake-up, and use the futex + * word's value (i.e., the user-space synchronization scheme) to decide whether + * to continue to block or not. + */ static inline void qemu_futex_wait(void *f, unsigned val) { while (qemu_futex(f, FUTEX_WAIT, (int) val, NULL, NULL, 0)) { |