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Date: Sat, 3 Jul 2010 10:43:23 +0100 From: Al Viro <viro@...IV.linux.org.uk> To: Frederic Weisbecker <fweisbec@...il.com> Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>, Andrew Morton <akpm@...ux-foundation.org>, reiserfs-devel@...r.kernel.org, linux-kernel@...r.kernel.org, Chris Mason <chris.mason@...cle.com>, Jeff Mahoney <jeffm@...freymahoney.com> Subject: Re: reiserfs locking (v2) On Sat, Jul 03, 2010 at 10:24:42AM +0100, Al Viro wrote: > Gyah... For the 1001st time: readdir() is far from being the only thing that > nests mmap_sem inside i_mutex. In particular, write() does the same thing. > > So yes, it *is* a real deadlock, TYVM, with no directories involved. Open the > same file twice, mmap one fd, close it, then have munmap() hitting i_mutex > in reiserfs_file_release() race with write() through another fd. > > Incidentally, reiserfs_file_release() checks in the fastpath look completely > bogus. Checking i_count? What the hell is that one about? And no, these > checks won't stop open() coming between them and grabbing i_mutex, so they > couldn't prevent the deadlock in question anyway. ... and unfortunately it's been that way since the the initial merge in 2.4.early. FWIW, it seems that i_count check was a misguided attempt to check that no other opened struct file are there, but it's a) wrong, since way, _way_ back - open() affects d_count, not i_count b) wrong even with such modification (consider hardlinks) c) wrong for even more reasons since forever - i_count and d_count could be bumped by many things at any time d) hopelessly racy anyway, since another open() could very well have happened just as we'd finished these checks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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