glibc: nptl Remove unnecessary catch-all-wake in condvar group switch

The following commits have been cherry-picked from Glibc master branch:
Bug : https://sourceware.org/bugzilla/show_bug.cgi?id=25847

Upstream-Status: Backport
[https://sourceware.org/git/?p=glibc.git;a=commit;h=b42cc6af11062c260c7dfa91f1c89891366fed3e]

(From OE-Core rev: 02f2ac08edb506ec43cec93a5b09f5e6d7df02ec)

Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/recipes-core/glibc/glibc/0026-PR25847-3.patch

@@ -0,0 +1,77 @@
+From 28a5082045429fdc5a4744d45fdc5b5202528eaa Mon Sep 17 00:00:00 2001
+From: Malte Skarupke <malteskarupke@fastmail.fm>
+Date: Mon, 16 Jun 2025 23:29:49 -0700
+Subject: [PATCH] nptl: Remove unnecessary catch-all-wake in condvar group
+ switch
+
+This wake is unnecessary. We only switch groups after every sleeper in a group
+has been woken. Sure, they may take a while to actually wake up and may still
+hold a reference, but waking them a second time doesn't speed that up. Instead
+this just makes the code more complicated and may hide problems.
+
+In particular this safety wake wouldn't even have helped with the bug that was
+fixed by Barrus' patch: The bug there was that pthread_cond_signal would not
+switch g1 when it should, so we wouldn't even have entered this code path.
+
+The following commits have been cherry-picked from Glibc master branch:
+Bug : https://sourceware.org/bugzilla/show_bug.cgi?id=25847
+
+Upstream-Status: Backport
+[https://sourceware.org/git/?p=glibc.git;a=commit;h=b42cc6af11062c260c7dfa91f1c89891366fed3e]
+
+Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com>
+---
+ nptl/pthread_cond_common.c | 30 +-----------------------------
+ 1 file changed, 1 insertion(+), 29 deletions(-)
+
+diff --git a/nptl/pthread_cond_common.c b/nptl/pthread_cond_common.c
+index 306a207dd6..f976a533a1 100644
+--- a/nptl/pthread_cond_common.c
++++ b/nptl/pthread_cond_common.c
+@@ -221,13 +221,7 @@ __condvar_quiesce_and_switch_g1 (pthread_cond_t *cond, uint64_t wseq,
+      * New waiters arriving concurrently with the group switching will all go
+        into G2 until we atomically make the switch.  Waiters existing in G2
+        are not affected.
+-     * Waiters in G1 have already received a signal and been woken. If they
+-       haven't woken yet, they will be closed out immediately by the advancing
+-       of __g_signals to the next "lowseq" (low 31 bits of the new g1_start),
+-       which will prevent waiters from blocking using a futex on
+-       __g_signals since it provides enough signals for all possible
+-       remaining waiters.  As a result, they can each consume a signal
+-       and they will eventually remove their group reference.  */
++     * Waiters in G1 have already received a signal and been woken.  */
+ 
+   /* Update __g1_start, which finishes closing this group.  The value we add
+      will never be negative because old_orig_size can only be zero when we
+@@ -240,28 +234,6 @@ __condvar_quiesce_and_switch_g1 (pthread_cond_t *cond, uint64_t wseq,
+ 
+   unsigned int lowseq = ((old_g1_start + old_orig_size) << 1) & ~1U;
+ 
+-  /* If any waiters still hold group references (and thus could be blocked),
+-     then wake them all up now and prevent any running ones from blocking.
+-     This is effectively a catch-all for any possible current or future
+-     bugs that can allow the group size to reach 0 before all G1 waiters
+-     have been awakened or at least given signals to consume, or any
+-     other case that can leave blocked (or about to block) older waiters..  */
+-  if ((atomic_fetch_or_release (cond->__data.__g_refs + g1, 0) >> 1) > 0)
+-   {
+-    /* First advance signals to the end of the group (i.e. enough signals
+-       for the entire G1 group) to ensure that waiters which have not
+-       yet blocked in the futex will not block.
+-       Note that in the vast majority of cases, this should never
+-       actually be necessary, since __g_signals will have enough
+-       signals for the remaining g_refs waiters.  As an optimization,
+-       we could check this first before proceeding, although that
+-       could still leave the potential for futex lost wakeup bugs
+-       if the signal count was non-zero but the futex wakeup
+-       was somehow lost.  */
+-    atomic_store_release (cond->__data.__g_signals + g1, lowseq);
+-
+-    futex_wake (cond->__data.__g_signals + g1, INT_MAX, private);
+-   }
+   /* At this point, the old G1 is now a valid new G2 (but not in use yet).
+      No old waiter can neither grab a signal nor acquire a reference without
+      noticing that __g1_start is larger.
+-- 
+2.49.0
+

meta/recipes-core/glibc/glibc_2.35.bb

@@ -64,6 +64,7 @@ SRC_URI =  "${GLIBC_GIT_URI};branch=${SRCBRANCH};name=glibc \
            file://0025-CVE-2025-4802.patch \
            file://0026-PR25847-1.patch \
            file://0026-PR25847-2.patch \
+           file://0026-PR25847-3.patch \
            \
            file://0001-Revert-Linux-Implement-a-useful-version-of-_startup_.patch \
            file://0002-get_nscd_addresses-Fix-subscript-typos-BZ-29605.patch \