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glib: reset errno to 0 when futex() returns EAGAIN

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This commit is contained in:
Daniel P. Berrange
2023-06-22 14:22:03 +00:00
committed by Philip Withnall
parent 3637c2c47f
commit 1bfc04a13d
2 changed files with 89 additions and 11 deletions
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42
glib/gthreadprivate.h
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@@ -54,6 +54,12 @@ struct _GRealThread
/* Wrapper macro to call `futex_time64` and/or `futex` with simple
* parameters and without returning the return value.
*
* We expect futex to sometimes return EAGAIN due to the race
* between the caller checking the current value and deciding to
* do the futex op. To avoid splattering errno on success, we
* restore the original errno if EAGAIN is seen. See also:
* https://gitlab.gnome.org/GNOME/glib/-/issues/3034
*
* If the `futex_time64` syscall does not exist (`ENOSYS`), we retry again
* with the normal `futex` syscall. This can happen if newer kernel headers
* are used than the kernel that is actually running.
@@ -70,23 +76,37 @@ struct _GRealThread
if (res < 0 && errno == ENOSYS) \
{ \
errno = saved_errno; \
syscall (__NR_futex, uaddr, (gsize) futex_op, __VA_ARGS__); \
res = syscall (__NR_futex, uaddr, (gsize) futex_op, __VA_ARGS__); \
} \
if (res < 0 && errno == EAGAIN) \
{ \
errno = saved_errno; \
} \
} \
G_STMT_END
#elif defined(__NR_futex_time64)
#define g_futex_simple(uaddr, futex_op, ...) \
G_STMT_START \
{ \
syscall (__NR_futex_time64, uaddr, (gsize) futex_op, __VA_ARGS__); \
} \
#define g_futex_simple(uaddr, futex_op, ...) \
G_STMT_START \
{ \
int saved_errno = errno; \
int res = syscall (__NR_futex_time64, uaddr, (gsize) futex_op, __VA_ARGS__); \
if (res < 0 && errno == EAGAIN) \
{ \
errno = saved_errno; \
} \
} \
G_STMT_END
#elif defined(__NR_futex)
#define g_futex_simple(uaddr, futex_op, ...) \
G_STMT_START \
{ \
syscall (__NR_futex, uaddr, (gsize) futex_op, __VA_ARGS__); \
} \
#define g_futex_simple(uaddr, futex_op, ...) \
G_STMT_START \
{ \
int saved_errno = errno; \
int res = syscall (__NR_futex, uaddr, (gsize) futex_op, __VA_ARGS__); \
if (res < 0 && errno == EAGAIN) \
{ \
errno = saved_errno; \
} \
} \
G_STMT_END
#else /* !defined(__NR_futex) && !defined(__NR_futex_time64) */
#error "Neither __NR_futex nor __NR_futex_time64 are defined but were found by meson"