From: Sunil Dora Date: Tue, 17 Jun 2025 10:08:51 +0000 (-0700) Subject: glibc: nptl Remove unnecessary quadruple check in pthread_cond_wait X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=761758340002f9dbff8e0668f4883ff623b232a0;p=thirdparty%2Fopenembedded%2Fopenembedded-core-contrib.git 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] Signed-off-by: Sunil Dora Signed-off-by: Steve Sakoman --- 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 +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 +--- + 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 \