From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
To: 'GNU C Library' <libc-alpha@sourceware.org>
Subject: [PATCH] Avoid RMW of flags2 outside lock (BZ #27842)
Date: Thu, 19 May 2022 15:10:22 +0000 [thread overview]
Message-ID: <DB6PR0801MB187958646D1DCDD920EA00F183D09@DB6PR0801MB1879.eurprd08.prod.outlook.com> (raw)
Remove an unconditional RMW on flags2 in flockfile - if _IO_FLAGS2_NEED_LOCK
is set, we are single-threaded and we can safely clear the flag. This fixes
BZ #27842.
---
diff --git a/stdio-common/flockfile.c b/stdio-common/flockfile.c
index a5decb450f8d477e3105d02661282afeab58f88b..7ba9ab59082d2c1dfba7d5e9a91175c9dec7ec49 100644
--- a/stdio-common/flockfile.c
+++ b/stdio-common/flockfile.c
@@ -22,7 +22,10 @@
void
__flockfile (FILE *stream)
{
- stream->_flags2 |= _IO_FLAGS2_NEED_LOCK;
+ /* If we're single-threaded, turn off single-thread optimizations
+ when locking a file. Avoid updating flags2 if multi-threaded. */
+ if (!_IO_need_lock (stream))
+ stream->_flags2 |= _IO_FLAGS2_NEED_LOCK;
_IO_lock_lock (*stream->_lock);
}
weak_alias (__flockfile, flockfile);
next reply other threads:[~2022-05-19 15:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-19 15:10 Wilco Dijkstra [this message]
2022-05-19 15:25 ` Andreas Schwab
2022-05-19 15:47 ` Adhemerval Zanella
2022-05-19 16:26 ` Wilco Dijkstra
2022-05-19 16:57 ` Adhemerval Zanella
2022-05-20 10:34 ` Wilco Dijkstra
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