diff options
Diffstat (limited to 'system/musl/fix-file-locking-race.patch')
| -rw-r--r-- | system/musl/fix-file-locking-race.patch | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/system/musl/fix-file-locking-race.patch b/system/musl/fix-file-locking-race.patch new file mode 100644 index 000000000..2ef91390a --- /dev/null +++ b/system/musl/fix-file-locking-race.patch @@ -0,0 +1,54 @@ +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: 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. +--- + 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; + } + +-- +cgit v1.2.1 + |