From: Jan Kara <jack@suse.cz>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org, Jan Kara <jack@suse.cz>,
Josh Boyer <jwboyer@redhat.com>, Dave Jones <davej@redhat.com>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Tyler Hicks <tyhicks@canonical.com>
Subject: Re: udf deadlock (was Re: hugetlbfs lockdep spew revisited.)
Date: Mon, 20 Feb 2012 17:01:35 +0100 [thread overview]
Message-ID: <20120220160135.GH6799@quack.suse.cz> (raw)
In-Reply-To: <20120217174818.GP23916@ZenIV.linux.org.uk>
On Fri 17-02-12 17:48:18, Al Viro wrote:
> On Fri, Feb 17, 2012 at 12:49:22AM +0000, Al Viro wrote:
> > Folks, this is not a false positive and it has nothing to do with misannotation
> > for directories. Deadlock is real; I have no idea WTF do we what ->i_mutex
> > held over that area in hugetlbfs ->mmap(), but doing that is really, really
> > wrong, whatever the reason.
>
> Arrrrgh... Some grepping around has uncovered another deadlock on
> i_mutex/mmap_sem and this one is not hard to hit at all.
>
> Thread A:
> opens file on UDF (O_RDWR open)
> does big, fat write() to it
> Thread B:
> opens the same file (also O_RDWR)
> mmaps it
> closes
> does munmap()
>
> and there we are - munmap() will end up closing the second struct file,
> call udf_release_file() and we are hitting ->i_mutex while under
> ->mmap_sem. Blocking on it, actually, since generic_file_aio_write()
> in the first thread is holding ->i_mutex. And as soon as thread A gets
> around to faulting the next piece of data in, well... To widen the
> window a lot, mmap something large sitting on NFS and do write() from
> that mmapped area. Race window as wide as one could ask for...
Right, I didn't realize ->release() may be called with mmap_sem held.
Thanks for spotting this. BTW: Documentation/filesystems/Locking might
need an update since it states:
locking rules:
All may block except for ->setlease.
No VFS locks held on entry except for ->setlease.
> What happens there is prealloc discard on close; do we even want ->i_mutex
> there these days? Note that there's also
> down_write(&UDF_I(inode)->i_data_sem);
> in udf_release_file()...
I've looked around and it seems we don't need i_mutex for anything.
i_data_sem should be enough. So I'll just remove i_mutex.
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
next prev parent reply other threads:[~2012-02-20 16:01 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-17 0:08 hugetlbfs lockdep spew revisited Dave Jones
2012-02-17 0:16 ` Josh Boyer
2012-02-17 0:34 ` Al Viro
2012-02-17 0:38 ` Tyler Hicks
2012-02-17 0:49 ` Al Viro
2012-02-17 3:42 ` Tyler Hicks
2012-02-21 18:21 ` Mimi Zohar
2012-02-17 6:47 ` J. R. Okajima
2012-02-17 17:48 ` udf deadlock (was Re: hugetlbfs lockdep spew revisited.) Al Viro
2012-02-20 16:01 ` Jan Kara [this message]
2012-02-18 10:55 ` hugetlbfs lockdep spew revisited Aneesh Kumar K.V
2012-02-17 0:27 ` Al Viro
2012-02-23 9:27 ` Aneesh Kumar K.V
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