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* [glibc/release/2.37/master] linux: Use rseq area unconditionally in sched_getcpu (bug 31479)
@ 2024-03-18 17:49 Arjun Shankar
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From: Arjun Shankar @ 2024-03-18 17:49 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=829b64598bc4e801d2e2878a5d0d0bcbd9314094
commit 829b64598bc4e801d2e2878a5d0d0bcbd9314094
Author: Florian Weimer <fweimer@redhat.com>
Date: Fri Mar 15 19:08:24 2024 +0100
linux: Use rseq area unconditionally in sched_getcpu (bug 31479)
Originally, nptl/descr.h included <sys/rseq.h>, but we removed that
in commit 2c6b4b272e6b4d07303af25709051c3e96288f2d ("nptl:
Unconditionally use a 32-byte rseq area"). After that, it was
not ensured that the RSEQ_SIG macro was defined during sched_getcpu.c
compilation that provided a definition. This commit always checks
the rseq area for CPU number information before using the other
approaches.
This adds an unnecessary (but well-predictable) branch on
architectures which do not define RSEQ_SIG, but its cost is small
compared to the system call. Most architectures that have vDSO
acceleration for getcpu also have rseq support.
Fixes: 2c6b4b272e6b4d07303af25709051c3e96288f2d
Fixes: 1d350aa06091211863e41169729cee1bca39f72f
Reviewed-by: Arjun Shankar <arjun@redhat.com>
(cherry picked from commit 7a76f218677d149d8b7875b336722108239f7ee9)
Fixes: 9da8174362860b4fc564c8ca8c11fc3c51ed1de9
Diff:
---
sysdeps/unix/sysv/linux/sched_getcpu.c | 8 --------
1 file changed, 8 deletions(-)
diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c
index 4457d714bc..22700ef846 100644
--- a/sysdeps/unix/sysv/linux/sched_getcpu.c
+++ b/sysdeps/unix/sysv/linux/sched_getcpu.c
@@ -33,17 +33,9 @@ vsyscall_sched_getcpu (void)
return r == -1 ? r : cpu;
}
-#ifdef RSEQ_SIG
int
sched_getcpu (void)
{
int cpu_id = THREAD_GETMEM_VOLATILE (THREAD_SELF, rseq_area.cpu_id);
return __glibc_likely (cpu_id >= 0) ? cpu_id : vsyscall_sched_getcpu ();
}
-#else /* RSEQ_SIG */
-int
-sched_getcpu (void)
-{
- return vsyscall_sched_getcpu ();
-}
-#endif /* RSEQ_SIG */
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