mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-12-04 03:25:02 +00:00
55 lines
1.9 KiB
Diff
55 lines
1.9 KiB
Diff
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
|
|
|