glibc: nptl Remove unnecessary quadruple check in pthread_cond_wait

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=4f7b051f8ee3feff1b53b27a906f245afaa9cee1]

(From OE-Core rev: 761758340002f9dbff8e0668f4883ff623b232a0)

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

2 files changed, 118 insertions, 0 deletions

diff --git a/meta/recipes-core/glibc/glibc/0026-PR25847-4.patch b/meta/recipes-core/glibc/glibc/0026-PR25847-4.patch
new file mode 100644
index 0000000000..f8674d62ae
--- /dev/null
+++ b/meta/recipes-core/glibc/glibc/0026-PR25847-4.patch
@@ -0,0 +1,117 @@
+From 16b9af737c77b153fca4f36cbdbe94f7416c0b42 Mon Sep 17 00:00:00 2001
+From: Malte Skarupke <malteskarupke@fastmail.fm>
+Date: Mon, 16 Jun 2025 23:38:40 -0700
+Subject: [PATCH] nptl: Remove unnecessary quadruple check in pthread_cond_wait
+
+pthread_cond_wait was checking whether it was in a closed group no less than
+four times. Checking once is enough. Here are the four checks:
+
+1. While spin-waiting. This was dead code: maxspin is set to 0 and has been
+   for years.
+2. Before deciding to go to sleep, and before incrementing grefs: I kept this
+3. After incrementing grefs. There is no reason to think that the group would
+   close while we do an atomic increment. Obviously it could close at any
+   point, but that doesn't mean we have to recheck after every step. This
+   check was equally good as check 2, except it has to do more work.
+4. When we find ourselves in a group that has a signal. We only get here after
+   we check that we're not in a closed group. There is no need to check again.
+   The check would only have helped in cases where the compare_exchange in the
+   next line would also have failed. Relying on the compare_exchange is fine.
+
+Removing the duplicate checks clarifies the code.
+
+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=4f7b051f8ee3feff1b53b27a906f245afaa9cee1]
+
+Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com>
+---
+ nptl/pthread_cond_wait.c | 49 ----------------------------------------
+ 1 file changed, 49 deletions(-)
+
+diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
+index cee1968756..47e834cade 100644
+--- a/nptl/pthread_cond_wait.c
++++ b/nptl/pthread_cond_wait.c
+@@ -366,7 +366,6 @@ static __always_inline int
+ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
+     clockid_t clockid, const struct __timespec64 *abstime)
+ {
+-  const int maxspin = 0;
+   int err;
+   int result = 0;
+ 
+@@ -425,33 +424,6 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
+          uint64_t g1_start = __condvar_load_g1_start_relaxed (cond);
+          unsigned int lowseq = (g1_start & 1) == g ? signals : g1_start & ~1U;
+ 
+-         /* Spin-wait first.
+-            Note that spinning first without checking whether a timeout
+-            passed might lead to what looks like a spurious wake-up even
+-            though we should return ETIMEDOUT (e.g., if the caller provides
+-            an absolute timeout that is clearly in the past).  However,
+-            (1) spurious wake-ups are allowed, (2) it seems unlikely that a
+-            user will (ab)use pthread_cond_wait as a check for whether a
+-            point in time is in the past, and (3) spinning first without
+-            having to compare against the current time seems to be the right
+-            choice from a performance perspective for most use cases.  */
+-         unsigned int spin = maxspin;
+-         while (spin > 0 && ((int)(signals - lowseq) < 2))
+-           {
+-             /* Check that we are not spinning on a group that's already
+-                closed.  */
+-             if (seq < (g1_start >> 1))
+-               break;
+-
+-             /* TODO Back off.  */
+-
+-             /* Reload signals.  See above for MO.  */
+-             signals = atomic_load_acquire (cond->__data.__g_signals + g);
+-             g1_start = __condvar_load_g1_start_relaxed (cond);
+-             lowseq = (g1_start & 1) == g ? signals : g1_start & ~1U;
+-             spin--;
+-           }
+-
+          if (seq < (g1_start >> 1))
+            {
+              /* If the group is closed already,
+@@ -482,24 +454,6 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
+             an atomic read-modify-write operation and thus extend the release
+             sequence.  */
+          atomic_fetch_add_acquire (cond->__data.__g_refs + g, 2);
+-         signals = atomic_load_acquire (cond->__data.__g_signals + g);
+-         g1_start = __condvar_load_g1_start_relaxed (cond);
+-         lowseq = (g1_start & 1) == g ? signals : g1_start & ~1U;
+-
+-         if (seq < (g1_start >> 1))
+-           {
+-             /* group is closed already, so don't block */
+-             __condvar_dec_grefs (cond, g, private);
+-             goto done;
+-           }
+-
+-         if ((int)(signals - lowseq) >= 2)
+-           {
+-             /* a signal showed up or G1/G2 switched after we grabbed the
+-                refcount */
+-             __condvar_dec_grefs (cond, g, private);
+-             break;
+-           }
+ 
+          // Now block.
+          struct _pthread_cleanup_buffer buffer;
+@@ -533,9 +487,6 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
+          /* Reload signals.  See above for MO.  */
+          signals = atomic_load_acquire (cond->__data.__g_signals + g);
+        }
+-
+-       if (seq < (__condvar_load_g1_start_relaxed (cond) >> 1))
+-        goto done;
+     }
+   /* Try to grab a signal.  See above for MO.  (if we do another loop
+      iteration we need to see the correct value of g1_start)  */
+-- 
+2.49.0
+
diff --git a/meta/recipes-core/glibc/glibc_2.35.bb b/meta/recipes-core/glibc/glibc_2.35.bb
index 5e1f45608e..bb5d22cfe8 100644
--- a/meta/recipes-core/glibc/glibc_2.35.bb
+++ b/meta/recipes-core/glibc/glibc_2.35.bb
@@ -65,6 +65,7 @@ SRC_URI =  "${GLIBC_GIT_URI};branch=${SRCBRANCH};name=glibc \
            file://0026-PR25847-1.patch \
            file://0026-PR25847-2.patch \
            file://0026-PR25847-3.patch \
+           file://0026-PR25847-4.patch \
            \
            file://0001-Revert-Linux-Implement-a-useful-version-of-_startup_.patch \
            file://0002-get_nscd_addresses-Fix-subscript-typos-BZ-29605.patch \