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47 lines
1.7 KiB
47 lines
1.7 KiB
1 month ago
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commit 71fcdba577884627c3ee4e43beb915da752efb1f
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Fri Mar 15 19:08:24 2024 +0100
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linux: Use rseq area unconditionally in sched_getcpu (bug 31479)
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Originally, nptl/descr.h included <sys/rseq.h>, but we removed that
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in commit 2c6b4b272e6b4d07303af25709051c3e96288f2d ("nptl:
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Unconditionally use a 32-byte rseq area"). After that, it was
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not ensured that the RSEQ_SIG macro was defined during sched_getcpu.c
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compilation that provided a definition. This commit always checks
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the rseq area for CPU number information before using the other
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approaches.
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This adds an unnecessary (but well-predictable) branch on
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architectures which do not define RSEQ_SIG, but its cost is small
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compared to the system call. Most architectures that have vDSO
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acceleration for getcpu also have rseq support.
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Fixes: 2c6b4b272e6b4d07303af25709051c3e96288f2d
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Fixes: 1d350aa06091211863e41169729cee1bca39f72f
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Reviewed-by: Arjun Shankar <arjun@redhat.com>
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(cherry picked from commit 7a76f218677d149d8b7875b336722108239f7ee9)
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diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c
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index dfb884568d154537..72a3360550b8667a 100644
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--- a/sysdeps/unix/sysv/linux/sched_getcpu.c
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+++ b/sysdeps/unix/sysv/linux/sched_getcpu.c
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@@ -33,17 +33,9 @@ vsyscall_sched_getcpu (void)
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return r == -1 ? r : cpu;
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}
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-#ifdef RSEQ_SIG
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int
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sched_getcpu (void)
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{
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int cpu_id = THREAD_GETMEM_VOLATILE (THREAD_SELF, rseq_area.cpu_id);
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return __glibc_likely (cpu_id >= 0) ? cpu_id : vsyscall_sched_getcpu ();
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}
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-#else /* RSEQ_SIG */
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-int
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-sched_getcpu (void)
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-{
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- return vsyscall_sched_getcpu ();
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-}
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-#endif /* RSEQ_SIG */
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