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Date: Sat, 17 Dec 2011 22:10:28 +0000 From: Al Viro <viro@...IV.linux.org.uk> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Djalal Harouni <tixxdz@...ndz.org>, Hugh Dickins <hughd@...gle.com>, Minchan Kim <minchan.kim@...il.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, "J. Bruce Fields" <bfields@...ldses.org>, Neil Brown <neilb@...e.de>, Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>, Christoph Hellwig <hch@...radead.org>, Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org Subject: Re: [PATCH] mm: add missing mutex lock arround notify_change On Sat, Dec 17, 2011 at 09:41:37PM +0000, Al Viro wrote: > xfs and ext4_ioctl() need to be fixed; XFS fix follows, ext4 I'd rather left > to ext4 folks - I don't know how wide an area needs i_mutex there Oh, for fsck sake... People, this is *obviously* broken - if nothing else, removing suid after modifying the file contents is too late. Moreover, this mext_inode_double_lock() thing is asking for trouble; it's deadlock-free only because nothing else takes i_mutex on more than one non-directory inode and does that as the innermost lock. Start calling it for directories (or have somebody cut'n'paste it and use it for directories) and you've got a nice, shiny deadlock... BTW, is ordering really needed in double_down_write_data_sem()? IOW, can we get contention between several callers of that thing? >From my reading of that code, all call chains leading to this sucker are guaranteed to already hold i_mutex on both inodes. If that is true, we don't need any ordering in double_down_write_data_sem() at all... AFAICS, the minimal fix is to move file_remove_suid() call into ext4_move_extents(), just after we have acquired i_mutex in there. Moreover, I think it should be done to *both* files, since both have contents modified. And I see no point in making that conditional... -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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