From: Christoph Hellwig <hch@infradead.org>
To: Theodore Ts'o <tytso@mit.edu>
Cc: Christoph Hellwig <hch@infradead.org>,
Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
bugzilla-daemon@bugzilla.kernel.org, meetmehiro@gmail.com,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [Bug 50981] generic_file_aio_read ?: No locking means DATA CORRUPTION read and write on same 4096 page range
Date: Mon, 26 Nov 2012 17:09:08 -0500 [thread overview]
Message-ID: <20121126220908.GA20733@infradead.org> (raw)
In-Reply-To: <20121126214937.GA21590@thunk.org>
On Mon, Nov 26, 2012 at 04:49:37PM -0500, Theodore Ts'o wrote:
> Christoph, can you give some kind of estimate for the overhead that
> adding this locking in XFS actually costs in practice?
I don't know any real life measurements, but in terms of implementation
the over head is:
a) taking a the rw_semaphore in shared mode for every buffered read
b) taking the slightly slower exclusive rw_semaphore for buffered writes
instead of the plain mutex
On the other hand it significantly simplifies the locking for direct
I/O and allows parallel direct I/O writers.
> And does XFS
> provide any kind of consistency guarantees if the reads/write overlap
> spans multiple pages? I assume the answer to that is no, correct?
The answer is yes as the lock is taken globally on the inode.
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Theodore Ts'o <tytso@mit.edu>
Cc: Christoph Hellwig <hch@infradead.org>,
Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
bugzilla-daemon@bugzilla.kernel.org, meetmehiro@gmail.com,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [Bug 50981] generic_file_aio_read ?: No locking means DATA CORRUPTION read and write on same 4096 page range
Date: Mon, 26 Nov 2012 17:09:08 -0500 [thread overview]
Message-ID: <20121126220908.GA20733@infradead.org> (raw)
In-Reply-To: <20121126214937.GA21590@thunk.org>
On Mon, Nov 26, 2012 at 04:49:37PM -0500, Theodore Ts'o wrote:
> Christoph, can you give some kind of estimate for the overhead that
> adding this locking in XFS actually costs in practice?
I don't know any real life measurements, but in terms of implementation
the over head is:
a) taking a the rw_semaphore in shared mode for every buffered read
b) taking the slightly slower exclusive rw_semaphore for buffered writes
instead of the plain mutex
On the other hand it significantly simplifies the locking for direct
I/O and allows parallel direct I/O writers.
> And does XFS
> provide any kind of consistency guarantees if the reads/write overlap
> spans multiple pages? I assume the answer to that is no, correct?
The answer is yes as the lock is taken globally on the inode.
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next prev parent reply other threads:[~2012-11-26 22:09 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-50981-5823@https.bugzilla.kernel.org/>
[not found] ` <20121126163328.ACEB011FE9C@bugzilla.kernel.org>
2012-11-26 16:45 ` [Bug 50981] generic_file_aio_read ?: No locking means DATA CORRUPTION read and write on same 4096 page range Theodore Ts'o
2012-11-26 16:45 ` Theodore Ts'o
2012-11-26 18:59 ` Hiro Lalwani
2012-11-26 20:05 ` Hugh Dickins
2012-11-26 20:05 ` Hugh Dickins
2012-11-26 20:13 ` Christoph Hellwig
2012-11-26 21:28 ` Dave Chinner
2012-11-26 21:39 ` Christoph Hellwig
2012-11-26 21:39 ` Christoph Hellwig
2012-11-26 21:49 ` Theodore Ts'o
2012-11-26 22:09 ` Christoph Hellwig [this message]
2012-11-26 22:09 ` Christoph Hellwig
2012-11-27 1:32 ` Theodore Ts'o
2012-11-27 4:27 ` Dave Chinner
2012-11-27 4:27 ` Dave Chinner
2012-11-26 22:17 ` Dave Chinner
2012-11-26 22:17 ` Dave Chinner
2012-11-26 20:15 ` Zach Brown
2012-11-25 16:31 [Bug 50981] New: ext4 : " bugzilla-daemon
2012-11-26 12:26 ` [Bug 50981] generic_file_aio_read ?: No locking means " bugzilla-daemon
2012-11-26 13:21 ` Theodore Ts'o
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