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authorGravatar Thomas Petazzoni <thomas.petazzoni@bootlin.com>2018-09-19 08:44:24 +0200
committerGravatar Peter Korsgaard <peter@korsgaard.com>2018-09-20 07:06:58 +0200
commit1f90976c88f1e4a910f2fb55a331e3fc1048d62d (patch)
tree5c7aef14c87d74a4eef19d124de6bc5a09748792
parentadc98bfa260569c844843934768b0ae77cf64a86 (diff)
downloadbuildroot-1f90976c88f1e4a910f2fb55a331e3fc1048d62d.tar.gz
buildroot-1f90976c88f1e4a910f2fb55a331e3fc1048d62d.tar.bz2
musl: add upstream patch to fix race condition in file locking
According to [1]: musl 1.1.20 introduced a regression in stdio FILE locking that can cause soft deadlocks with >2 threads contending for a FILE. Users/dists should apply https://git.musl-libc.org/cgit/musl/commit/?id=0db393d3a77bb9f300a356c6a5484fc2dddb161d. [1] https://twitter.com/musllibc/status/1042292786568024070 This commit therefore adds the corresponding patch to the musl package. Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com> Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
-rw-r--r--package/musl/0002-fix-race-condition-in-file-locking.patch55
1 files changed, 55 insertions, 0 deletions
diff --git a/package/musl/0002-fix-race-condition-in-file-locking.patch b/package/musl/0002-fix-race-condition-in-file-locking.patch
new file mode 100644
index 0000000000..f3e85e6888
--- /dev/null
+++ b/package/musl/0002-fix-race-condition-in-file-locking.patch
@@ -0,0 +1,55 @@
+From 0db393d3a77bb9f300a356c6a5484fc2dddb161d Mon Sep 17 00:00:00 2001
+From: Kaarle Ritvanen <kaarle.ritvanen@datakunkku.fi>
+Date: Tue, 18 Sep 2018 10:03:27 +0300
+Subject: [PATCH] fix race condition in file locking
+
+The condition occurs when
+- thread #1 is holding the lock
+- thread #2 is waiting for it on __futexwait
+- thread #1 is about to release the lock and performs a_swap
+- thread #3 enters the __lockfile function and manages to grab the lock
+ before thread #1 calls __wake, resetting the MAYBE_WAITERS flag
+- thread #1 calls __wake
+- thread #2 wakes up but goes again to __futexwait as the lock is
+ held by thread #3
+- thread #3 releases the lock but does not call __wake as the
+ MAYBE_WAITERS flag is not set
+
+This condition results in thread #2 not being woken up. This patch fixes
+the problem by making the woken up thread ensure that the flag is
+properly set before going to sleep again.
+
+Mainainer's note: This fixes a regression introduced in commit
+c21f750727515602a9e84f2a190ee8a0a2aeb2a1.
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
+---
+ src/stdio/__lockfile.c | 12 ++++++------
+ 1 file changed, 6 insertions(+), 6 deletions(-)
+
+diff --git a/src/stdio/__lockfile.c b/src/stdio/__lockfile.c
+index 2ff75d8a..0dcb2a42 100644
+--- a/src/stdio/__lockfile.c
++++ b/src/stdio/__lockfile.c
+@@ -8,13 +8,13 @@ int __lockfile(FILE *f)
+ int owner = f->lock, tid = __pthread_self()->tid;
+ if ((owner & ~MAYBE_WAITERS) == tid)
+ return 0;
+- for (;;) {
+- owner = a_cas(&f->lock, 0, tid);
+- if (!owner) return 1;
+- if (a_cas(&f->lock, owner, owner|MAYBE_WAITERS)==owner) break;
++ owner = a_cas(&f->lock, 0, tid);
++ if (!owner) return 1;
++ while ((owner = a_cas(&f->lock, 0, tid|MAYBE_WAITERS))) {
++ if ((owner & MAYBE_WAITERS) ||
++ a_cas(&f->lock, owner, owner|MAYBE_WAITERS)==owner)
++ __futexwait(&f->lock, owner|MAYBE_WAITERS, 1);
+ }
+- while ((owner = a_cas(&f->lock, 0, tid|MAYBE_WAITERS)))
+- __futexwait(&f->lock, owner, 1);
+ return 1;
+ }
+
+--
+2.14.4
+