From: Dave Chinner <david@fromorbit.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Djalal Harouni <tixxdz@opendz.org>,
Hugh Dickins <hughd@google.com>,
Minchan Kim <minchan.kim@gmail.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Wu Fengguang <fengguang.wu@intel.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
"J. Bruce Fields" <bfields@fieldses.org>,
Neil Brown <neilb@suse.de>,
Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>,
Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] mm: add missing mutex lock arround notify_change
Date: Mon, 19 Dec 2011 16:07:10 +1100 [thread overview]
Message-ID: <20111219050710.GQ23662@dastard> (raw)
In-Reply-To: <20111219020637.GA1653@ZenIV.linux.org.uk>
On Mon, Dec 19, 2011 at 02:06:37AM +0000, Al Viro wrote:
> On Mon, Dec 19, 2011 at 02:03:40AM +0000, Al Viro wrote:
>
> > OK, I'm definitely missing something. The very first thing
> > xfs_file_aio_write_checks() does is
> > xfs_rw_ilock(ip, XFS_ILOCK_EXCL);
> > which really makes me wonder how the hell does that manage to avoid an
> > instant deadlock in case of call via xfs_file_buffered_aio_write()
> > where we have:
> > struct address_space *mapping = file->f_mapping;
> > struct inode *inode = mapping->host;
> > struct xfs_inode *ip = XFS_I(inode);
> > *iolock = XFS_IOLOCK_EXCL;
> > xfs_rw_ilock(ip, *iolock);
> > ret = xfs_file_aio_write_checks(file, &pos, &count, new_size, iolock);
> > which leads to
> > struct inode *inode = file->f_mapping->host;
> > struct xfs_inode *ip = XFS_I(inode);
> > (IOW, inode and ip are the same as in the caller) followed by
> > xfs_rw_ilock(ip, XFS_ILOCK_EXCL);
> > and with both xfs_rw_ilock() calls turning into
> > mutex_lock(&VFS_I(ip)->i_mutex);
> > xfs_ilock(ip, XFS_ILOCK_EXCL);
> > we ought to deadlock on that i_mutex. What am I missing and how do we manage
> > to survive that?
>
> Arrrgh... OK, I see... What I missed is that XFS_IOLOCK_EXCL is not
> XFS_ILOCK_EXCL. Nice naming, that...
Been that way for 15 years. :/
However, the naming makes sense to me - the IO lock is for
serialising IO operations on the inode, while the I lock is for
serialising metadata operations on the inode. I guess I'm used to
it, though, so I'll conceed that it might look strange/confusing to
someone who only occassionally looks at the internal XFS locking
code....
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
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next prev parent reply other threads:[~2011-12-19 5:07 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-16 11:25 [PATCH] mm: add missing mutex lock arround notify_change Djalal Harouni
2011-12-16 20:55 ` Andrew Morton
2011-12-16 21:54 ` Djalal Harouni
2011-12-17 21:41 ` Al Viro
2011-12-17 22:10 ` Al Viro
2011-12-20 22:09 ` Ted Ts'o
2011-12-20 22:45 ` Ted Ts'o
2011-12-19 1:43 ` Dave Chinner
2011-12-19 2:03 ` Al Viro
2011-12-19 2:06 ` Al Viro
2011-12-19 5:07 ` Dave Chinner [this message]
2011-12-19 4:22 ` Dave Chinner
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