--- /dev/null
+From f904a81ff8d0469ceaf3220329e716c03fcbd2d3 Mon Sep 17 00:00:00 2001
+From: Malte Skarupke <malteskarupke@fastmail.fm>
+Date: Tue, 14 Oct 2025 05:59:02 -0700
+Subject: [PATCH] nptl: Remove g_refs from condition variables
+
+This variable used to be needed to wait in group switching until all sleepers
+have confirmed that they have woken. This is no longer needed. Nothing waits
+on this variable so there is no need to track how many threads are currently
+asleep in each group.
+
+The following commits have been cherry-picked from Glibc master branch:
+Bug : https://sourceware.org/bugzilla/show_bug.cgi?id=25847
+cmmit: c36fc50781995e6758cae2b6927839d0157f213c
+
+Upstream-Status: Submitted
+[https://sourceware.org/pipermail/libc-stable/2025-July/002278.html]
+
+Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com>
+---
+ nptl/pthread_cond_wait.c | 52 +------------------------
+ nptl/tst-cond22.c | 12 +++---
+ sysdeps/nptl/bits/thread-shared-types.h | 3 +-
+ sysdeps/nptl/pthread.h | 2 +-
+ 4 files changed, 9 insertions(+), 60 deletions(-)
+
+diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
+index 47e834ca..8a9219e0 100644
+--- a/nptl/pthread_cond_wait.c
++++ b/nptl/pthread_cond_wait.c
+@@ -143,23 +143,6 @@ __condvar_cancel_waiting (pthread_cond_t *cond, uint64_t seq, unsigned int g,
+ }
+ }
+
+-/* Wake up any signalers that might be waiting. */
+-static void
+-__condvar_dec_grefs (pthread_cond_t *cond, unsigned int g, int private)
+-{
+- /* Release MO to synchronize-with the acquire load in
+- __condvar_quiesce_and_switch_g1. */
+- if (atomic_fetch_add_release (cond->__data.__g_refs + g, -2) == 3)
+- {
+- /* Clear the wake-up request flag before waking up. We do not need more
+- than relaxed MO and it doesn't matter if we apply this for an aliased
+- group because we wake all futex waiters right after clearing the
+- flag. */
+- atomic_fetch_and_relaxed (cond->__data.__g_refs + g, ~(unsigned int) 1);
+- futex_wake (cond->__data.__g_refs + g, INT_MAX, private);
+- }
+-}
+-
+ /* Clean-up for cancellation of waiters waiting for normal signals. We cancel
+ our registration as a waiter, confirm we have woken up, and re-acquire the
+ mutex. */
+@@ -171,8 +154,6 @@ __condvar_cleanup_waiting (void *arg)
+ pthread_cond_t *cond = cbuffer->cond;
+ unsigned g = cbuffer->wseq & 1;
+
+- __condvar_dec_grefs (cond, g, cbuffer->private);
+-
+ __condvar_cancel_waiting (cond, cbuffer->wseq >> 1, g, cbuffer->private);
+ /* FIXME With the current cancellation implementation, it is possible that
+ a thread is cancelled after it has returned from a syscall. This could
+@@ -327,15 +308,6 @@ __condvar_cleanup_waiting (void *arg)
+ sufficient because if a waiter can see a sufficiently large value, it could
+ have also consume a signal in the waiters group.
+
+- It is essential that the last field in pthread_cond_t is __g_signals[1]:
+- The previous condvar used a pointer-sized field in pthread_cond_t, so a
+- PTHREAD_COND_INITIALIZER from that condvar implementation might only
+- initialize 4 bytes to zero instead of the 8 bytes we need (i.e., 44 bytes
+- in total instead of the 48 we need). __g_signals[1] is not accessed before
+- the first group switch (G2 starts at index 0), which will set its value to
+- zero after a harmless fetch-or whose return value is ignored. This
+- effectively completes initialization.
+-
+
+ Limitations:
+ * This condvar isn't designed to allow for more than
+@@ -440,21 +412,6 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
+ if ((int)(signals - lowseq) >= 2)
+ break;
+
+- /* No signals available after spinning, so prepare to block.
+- We first acquire a group reference and use acquire MO for that so
+- that we synchronize with the dummy read-modify-write in
+- __condvar_quiesce_and_switch_g1 if we read from that. In turn,
+- in this case this will make us see the advancement of __g_signals
+- to the upcoming new g1_start that occurs with a concurrent
+- attempt to reuse the group's slot.
+- We use acquire MO for the __g_signals check to make the
+- __g1_start check work (see spinning above).
+- Note that the group reference acquisition will not mask the
+- release MO when decrementing the reference count because we use
+- an atomic read-modify-write operation and thus extend the release
+- sequence. */
+- atomic_fetch_add_acquire (cond->__data.__g_refs + g, 2);
+-
+ // Now block.
+ struct _pthread_cleanup_buffer buffer;
+ struct _condvar_cleanup_buffer cbuffer;
+@@ -471,18 +428,11 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
+
+ if (__glibc_unlikely (err == ETIMEDOUT || err == EOVERFLOW))
+ {
+- __condvar_dec_grefs (cond, g, private);
+- /* If we timed out, we effectively cancel waiting. Note that
+- we have decremented __g_refs before cancellation, so that a
+- deadlock between waiting for quiescence of our group in
+- __condvar_quiesce_and_switch_g1 and us trying to acquire
+- the lock during cancellation is not possible. */
++ /* If we timed out, we effectively cancel waiting. */
+ __condvar_cancel_waiting (cond, seq, g, private);
+ result = err;
+ goto done;
+ }
+- else
+- __condvar_dec_grefs (cond, g, private);
+
+ /* Reload signals. See above for MO. */
+ signals = atomic_load_acquire (cond->__data.__g_signals + g);
+diff --git a/nptl/tst-cond22.c b/nptl/tst-cond22.c
+index 1336e9c7..bdcb45c5 100644
+--- a/nptl/tst-cond22.c
++++ b/nptl/tst-cond22.c
+@@ -106,13 +106,13 @@ do_test (void)
+ status = 1;
+ }
+
+- printf ("cond = { 0x%x:%x, 0x%x:%x, %u/%u/%u, %u/%u/%u, %u, %u }\n",
++ printf ("cond = { 0x%x:%x, 0x%x:%x, %u/%u, %u/%u, %u, %u }\n",
+ c.__data.__wseq.__value32.__high,
+ c.__data.__wseq.__value32.__low,
+ c.__data.__g1_start.__value32.__high,
+ c.__data.__g1_start.__value32.__low,
+- c.__data.__g_signals[0], c.__data.__g_refs[0], c.__data.__g_size[0],
+- c.__data.__g_signals[1], c.__data.__g_refs[1], c.__data.__g_size[1],
++ c.__data.__g_signals[0], c.__data.__g_size[0],
++ c.__data.__g_signals[1], c.__data.__g_size[1],
+ c.__data.__g1_orig_size, c.__data.__wrefs);
+
+ if (pthread_create (&th, NULL, tf, (void *) 1l) != 0)
+@@ -152,13 +152,13 @@ do_test (void)
+ status = 1;
+ }
+
+- printf ("cond = { 0x%x:%x, 0x%x:%x, %u/%u/%u, %u/%u/%u, %u, %u }\n",
++ printf ("cond = { 0x%x:%x, 0x%x:%x, %u/%u, %u/%u, %u, %u }\n",
+ c.__data.__wseq.__value32.__high,
+ c.__data.__wseq.__value32.__low,
+ c.__data.__g1_start.__value32.__high,
+ c.__data.__g1_start.__value32.__low,
+- c.__data.__g_signals[0], c.__data.__g_refs[0], c.__data.__g_size[0],
+- c.__data.__g_signals[1], c.__data.__g_refs[1], c.__data.__g_size[1],
++ c.__data.__g_signals[0], c.__data.__g_size[0],
++ c.__data.__g_signals[1], c.__data.__g_size[1],
+ c.__data.__g1_orig_size, c.__data.__wrefs);
+
+ return status;
+diff --git a/sysdeps/nptl/bits/thread-shared-types.h b/sysdeps/nptl/bits/thread-shared-types.h
+index 5653507e..6f17afa4 100644
+--- a/sysdeps/nptl/bits/thread-shared-types.h
++++ b/sysdeps/nptl/bits/thread-shared-types.h
+@@ -95,8 +95,7 @@ struct __pthread_cond_s
+ {
+ __atomic_wide_counter __wseq;
+ __atomic_wide_counter __g1_start;
+- unsigned int __g_refs[2] __LOCK_ALIGNMENT;
+- unsigned int __g_size[2];
++ unsigned int __g_size[2] __LOCK_ALIGNMENT;
+ unsigned int __g1_orig_size;
+ unsigned int __wrefs;
+ unsigned int __g_signals[2];
+diff --git a/sysdeps/nptl/pthread.h b/sysdeps/nptl/pthread.h
+index dedad4ec..bbb36540 100644
+--- a/sysdeps/nptl/pthread.h
++++ b/sysdeps/nptl/pthread.h
+@@ -152,7 +152,7 @@ enum
+
+
+ /* Conditional variable handling. */
+-#define PTHREAD_COND_INITIALIZER { { {0}, {0}, {0, 0}, {0, 0}, 0, 0, {0, 0} } }
++#define PTHREAD_COND_INITIALIZER { { {0}, {0}, {0, 0}, 0, 0, {0, 0} } }
+
+
+ /* Cleanup buffers */
+--
+2.49.0
+
projects / thirdparty / openembedded / openembedded-core.git / commitdiff
