The patch titled
futex: comment requeue key reference semantics
has been added to the -mm tree. Its filename is
futex-comment-requeue-key-reference-semantics.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: futex: comment requeue key reference semantics
From: Darren Hart <dvhltc@xxxxxxxxxx>
We've tripped over the futex_requeue drop_count refering to key2
instead of key1. The code is actually correct, but is non-intuitive.
This patch adds an explicit comment explaining the requeue.
Signed-off-by: Darren Hart <dvhltc@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/futex.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff -puN kernel/futex.c~futex-comment-requeue-key-reference-semantics kernel/futex.c
--- a/kernel/futex.c~futex-comment-requeue-key-reference-semantics
+++ a/kernel/futex.c
@@ -927,7 +927,12 @@ out_unlock:
if (hb1 != hb2)
spin_unlock(&hb2->lock);
- /* drop_futex_key_refs() must be called outside the spinlocks. */
+ /*
+ * drop_futex_key_refs() must be called outside the spinlocks. During
+ * the requeue we moved futex_q's from the hash bucket at key1 to the
+ * one at key2 and updated their key pointer. We no longer need to
+ * hold the references to key1.
+ */
while (--drop_count >= 0)
drop_futex_key_refs(&key1);
_
Patches currently in -mm which might be from dvhltc@xxxxxxxxxx are
futex-comment-requeue-key-reference-semantics.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
