pthread_cond_broadcast: Fix waiters-after-spinning case [BZ #23538]

(cherry picked from commit 99ea93ca31795469d2a1f1570f17a5c39c2eb7e2)

diff --git a/ChangeLog b/ChangeLog
index b9e732a1925ad4c58cf2c659b811577817210730..ef837778331b34625f144f13bb06a85dc40e48ed 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2018-08-27 Martin Kuchta  <martin.kuchta@netapp.com>
+          Torvald Riegel  <triegel@redhat.com>
+
+       [BZ #23538]
+       * nptl/pthread_cond_common.c (__condvar_quiesce_and_switch_g1):
+       Update r to include the set wake-request flag if waiters are
+       remaining after spinning.
+
 2018-08-03  DJ Delorie  <dj@redhat.com>
 
        * sysdeps/riscv/rvf/math_private.h (libc_feholdexcept_setround_riscv):

diff --git a/NEWS b/NEWS
index 873cf8f64fc03a722d5956890f1c40251e661ec7..3073712cbac0cf066bcfdd6aa536f8c2816b4287 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -11,6 +11,7 @@ The following bugs are resolved with this release:
 
   [23497] readdir64@GLIBC_2.1 cannot parse the kernel directory stream
   [23521] nss_files aliases database file stream leak
+  [23538] pthread_cond_broadcast: Fix waiters-after-spinning case
 
 \f
 Version 2.28

diff --git a/nptl/pthread_cond_common.c b/nptl/pthread_cond_common.c
index 8e425eb01eceabec64e2bad3cfeb2ec51b6f6d72..479e54febb41767596c85c3312716b6c52c8700a 100644 (file)
--- a/nptl/pthread_cond_common.c
+++ b/nptl/pthread_cond_common.c
@@ -405,8 +405,12 @@ __condvar_quiesce_and_switch_g1 (pthread_cond_t *cond, uint64_t wseq,
        {
          /* There is still a waiter after spinning.  Set the wake-request
             flag and block.  Relaxed MO is fine because this is just about
-            this futex word.  */
-         r = atomic_fetch_or_relaxed (cond->__data.__g_refs + g1, 1);
+            this futex word.
+
+            Update r to include the set wake-request flag so that the upcoming
+            futex_wait only blocks if the flag is still set (otherwise, we'd
+            violate the basic client-side futex protocol).  */
+         r = atomic_fetch_or_relaxed (cond->__data.__g_refs + g1, 1) | 1;
 
          if ((r >> 1) > 0)
            futex_wait_simple (cond->__data.__g_refs + g1, r, private);