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musl: apply upstream fix for file locking race

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This commit is contained in:
Will Dietz 2018-09-18 17:11:12 -05:00
parent ea326dd4b5
commit 4305e7d5ec
2 changed files with 57 additions and 0 deletions
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3
pkgs/os-specific/linux/musl/default.nix
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@ -56,6 +56,9 @@ stdenv.mkDerivation rec {
url = https://raw.githubusercontent.com/openwrt/openwrt/87606e25afac6776d1bbc67ed284434ec5a832b4/toolchain/musl/patches/300-relative.patch;
sha256 = "0hfadrycb60sm6hb6by4ycgaqc9sgrhh42k39v8xpmcvdzxrsq2n";
})
# Upstream bugfix, see: https://git.musl-libc.org/cgit/musl/commit/?id=0db393d3a77bb9f300a356c6a5484fc2dddb161d
# Explicitly flagged for inclusion by distributions using musl
./fix-file-locking-race.patch
];
preConfigure = ''
configureFlagsArray+=("--syslibdir=$out/lib")

54
pkgs/os-specific/linux/musl/fix-file-locking-race.patch Normal file
View file

@ -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;
}
--
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