Fix missing rseq acceleration for sched_getcpu (RHEL-28119)

Resolves: RHEL-28119

glibc-RHEL-28119.patch

@@ -0,0 +1,45 @@
+commit 7a76f218677d149d8b7875b336722108239f7ee9
+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>
+
+diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c
+index 6f78edaea1495342..a33e30a1cb8e161b 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 */

glibc.spec

@@ -157,7 +157,7 @@ end \
 Summary: The GNU libc libraries
 Name: glibc
 Version: %{glibcversion}
-Release: 176%{?dist}
+Release: 177%{?dist}
 
 # In general, GPLv2+ is used by programs, LGPLv2+ is used for
 # libraries.
@@ -1148,6 +1148,7 @@ Patch840: glibc-RHEL-56627-5.patch
 Patch841: glibc-RHEL-56627-6.patch
 Patch842: glibc-RHEL-56627-7.patch
 Patch843: glibc-RHEL-56627-8.patch
+Patch844: glibc-RHEL-28119.patch
 
 ##############################################################################
 # Continued list of core "glibc" package information:
@@ -3141,6 +3142,9 @@ update_gconv_modules_cache ()
 %endif
 
 %changelog
+* Fri Mar 14 2025 Arjun Shankar <arjun@redhat.com> - 2.34-177
+- Fix missing rseq acceleration for sched_getcpu (RHEL-28119)
+
 * Wed Mar 12 2025 Florian Weimer <fweimer@redhat.com> - 2.34-176
 - Add sched_setattr, sched_getattr, pthread_gettid_np (RHEL-56627, RHEL-83017)