From: Diogo Behrens <diogo.behrens@huawei.com>
To: Phil Yang <phil.yang@arm.com>
Cc: <dev@dpdk.org>
Subject: [dpdk-dev] [PATCH] librte_eal: fix mcslock hang on weak memory
Date: Wed, 26 Aug 2020 11:20:02 +0200 [thread overview]
Message-ID: <20200826092002.19395-1-diogo.behrens@huawei.com> (raw)
The initialization me->locked=1 in lock() must happen before
next->locked=0 in unlock(), otherwise a thread may hang forever,
waiting me->locked become 0. On weak memory systems (such as ARMv8),
the current implementation allows me->locked=1 to be reordered with
announcing the node (pred->next=me) and, consequently, to be
reordered with next->locked=0 in unlock().
This fix adds a release barrier to pred->next=me, forcing
me->locked=1 to happen before this operation.
Signed-off-by: Diogo Behrens <diogo.behrens@huawei.com>
---
lib/librte_eal/include/generic/rte_mcslock.h | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/lib/librte_eal/include/generic/rte_mcslock.h b/lib/librte_eal/include/generic/rte_mcslock.h
index 2bef28351..ce553f547 100644
--- a/lib/librte_eal/include/generic/rte_mcslock.h
+++ b/lib/librte_eal/include/generic/rte_mcslock.h
@@ -68,7 +68,14 @@ rte_mcslock_lock(rte_mcslock_t **msl, rte_mcslock_t *me)
*/
return;
}
- __atomic_store_n(&prev->next, me, __ATOMIC_RELAXED);
+ /* The store to me->next above should also complete before the node is
+ * visible to predecessor thread releasing the lock. Hence, the store
+ * prev->next also requires release semantics. Note that, for example,
+ * on ARM, the release semantics in the exchange operation is not
+ * strong as a release fence and is not sufficient to enforce the
+ * desired order here.
+ */
+ __atomic_store_n(&prev->next, me, __ATOMIC_RELEASE);
/* The while-load of me->locked should not move above the previous
* store to prev->next. Otherwise it will cause a deadlock. Need a
--
2.28.0
next reply other threads:[~2020-08-26 9:20 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-26 9:20 Diogo Behrens [this message]
2020-08-26 10:17 ` Phil Yang
2020-08-27 8:56 ` Diogo Behrens
2020-08-28 9:19 ` Phil Yang
2020-08-31 18:45 ` Honnappa Nagarahalli
2020-10-06 21:49 ` Thomas Monjalon
2020-10-07 9:55 ` Diogo Behrens
2020-10-20 11:56 ` Thomas Monjalon
2020-10-20 21:49 ` Honnappa Nagarahalli
2020-11-22 18:07 ` Thomas Monjalon
2020-11-23 15:06 ` Honnappa Nagarahalli
2020-11-23 15:44 ` Stephen Hemminger
2020-11-23 18:16 ` Honnappa Nagarahalli
2020-11-23 18:29 ` Honnappa Nagarahalli
2020-11-23 19:36 ` Stephen Hemminger
2020-11-25 4:50 ` Honnappa Nagarahalli
2020-11-25 8:41 ` Diogo Behrens
2020-11-25 14:16 ` Thomas Monjalon
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=20200826092002.19395-1-diogo.behrens@huawei.com \
--to=diogo.behrens@huawei.com \
--cc=dev@dpdk.org \
--cc=phil.yang@arm.com \
/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;
as well as URLs for NNTP newsgroup(s).