From: Mateusz Guzik <mguzik@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
mingo@kernel.org, hpa@zytor.com, torvalds@linux-foundation.org
Subject: [PATCH] locking/barriers: evaluate the argument to lockless_dereference only once
Date: Tue, 7 Jun 2016 15:14:55 +0200 [thread overview]
Message-ID: <1465305295-16336-1-git-send-email-mguzik@redhat.com> (raw)
The commit 25841ee0e9d2a ("Validate lockless_dereference() is used on a
pointer type") added a second use of the parameter to the macro.
This leads to trouble with consumers which use arguments with side
effects.
Instead, reuse the value which was read the first time.
Signed-off-by: Mateusz Guzik <mguzik@redhat.com>
---
include/linux/compiler.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index e9c6417..06f27fd 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -551,8 +551,8 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
*/
#define lockless_dereference(p) \
({ \
- __maybe_unused const void * const _________p2 = p; \
typeof(p) _________p1 = READ_ONCE(p); \
+ __maybe_unused const void * const _________p2 = _________p1; \
smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
(_________p1); \
})
--
1.8.3.1
next reply other threads:[~2016-06-07 13:15 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-07 13:14 Mateusz Guzik [this message]
2016-06-14 10:50 ` Peter Zijlstra
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1465305295-16336-1-git-send-email-mguzik@redhat.com \
--to=mguzik@redhat.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®