From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Subject: Re: do we need that smp_wmb() in __d_alloc()?
Date: Thu, 10 Mar 2016 21:17:29 +0000 [thread overview]
Message-ID: <20160310211729.GN17997@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20160310203428.GM17997@ZenIV.linux.org.uk>
On Thu, Mar 10, 2016 at 08:34:28PM +0000, Al Viro wrote:
> Speaking of barriers - why do we need one there at all? In __d_alloc(), that
> is. Look: callers of __d_alloc() are:
> * d_alloc() - cycles parent's ->d_lock, inserts into the list of
> parent's children. Anyone observing it on that list of children will be
> holding the same parent's ->d_lock. And anyone finding it in any other way
> will have to observe the effect of store done after the write barrier in
> spin_unlock.
... which still leaves the possibility of both stores migrating inside the
lock/unlock pair and past each other. IOW,
lock parent's d_lock
lock child's d_lock
put into hash
store terminating NUL in ->d_name
unlock parent's d_lock
unlock child's d_lock
is a possible sequence of events, with RCU access on another CPU observing
the damn without seeing the NUL-terminated name ;-/
Oh, well...
next prev parent reply other threads:[~2016-03-10 21:17 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-08 16:05 races in ll_splice_alias() Al Viro
2016-03-08 20:44 ` Drokin, Oleg
2016-03-08 21:11 ` Al Viro
2016-03-08 23:18 ` Drokin, Oleg
2016-03-09 0:34 ` Al Viro
2016-03-09 0:53 ` Drokin, Oleg
2016-03-09 1:26 ` Al Viro
2016-03-09 5:20 ` Drokin, Oleg
2016-03-09 23:47 ` Drokin, Oleg
2016-03-10 2:20 ` races in ll_splice_alias() and elsewhere (ext4, ocfs2) Al Viro
2016-03-10 2:59 ` Al Viro
2016-03-10 23:55 ` Theodore Ts'o
2016-03-11 3:18 ` Al Viro
2016-03-11 15:42 ` Theodore Ts'o
2016-03-10 3:08 ` Drokin, Oleg
2016-03-10 3:34 ` Al Viro
2016-03-10 3:46 ` Drokin, Oleg
2016-03-10 4:22 ` Drokin, Oleg
2016-03-10 4:43 ` Al Viro
2016-03-10 5:15 ` Al Viro
2016-03-11 3:47 ` Drokin, Oleg
2016-03-10 5:47 ` Drokin, Oleg
2016-03-10 19:59 ` Al Viro
2016-03-10 20:34 ` do we need that smp_wmb() in __d_alloc()? Al Viro
2016-03-10 21:17 ` Al Viro [this message]
2016-03-10 21:22 ` races in ll_splice_alias() and elsewhere (ext4, ocfs2) Drokin, Oleg
2016-03-10 23:23 ` Al Viro
2016-03-11 3:25 ` Drokin, Oleg
2016-03-12 17:22 ` Al Viro
2016-03-13 14:35 ` Sage Weil
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