diff options
Diffstat (limited to 'main/musl/0001-fix-race-condition-in-file-locking.patch')
| -rw-r--r-- | main/musl/0001-fix-race-condition-in-file-locking.patch | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/main/musl/0001-fix-race-condition-in-file-locking.patch b/main/musl/0001-fix-race-condition-in-file-locking.patch new file mode 100644 index 0000000000..c6ec9a5e6e --- /dev/null +++ b/main/musl/0001-fix-race-condition-in-file-locking.patch @@ -0,0 +1,51 @@ +From b6b592d75f694958424b8a4fbd909b52317651f1 Mon Sep 17 00:00:00 2001 +From: Kaarle Ritvanen <kaarle.ritvanen@datakunkku.fi> +Date: Tue, 18 Sep 2018 01:10:32 +0300 +Subject: [PATCH v2] 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. +--- + 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 + |