From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx103.postini.com [74.125.245.103]) by kanga.kvack.org (Postfix) with SMTP id B602E6B004F for ; Sat, 17 Dec 2011 17:10:37 -0500 (EST) Date: Sat, 17 Dec 2011 22:10:28 +0000 From: Al Viro Subject: Re: [PATCH] mm: add missing mutex lock arround notify_change Message-ID: <20111217221028.GZ2203@ZenIV.linux.org.uk> References: <20111216112534.GA13147@dztty> <20111216125556.db2bf308.akpm@linux-foundation.org> <20111217214137.GY2203@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111217214137.GY2203@ZenIV.linux.org.uk> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Djalal Harouni , Hugh Dickins , Minchan Kim , KAMEZAWA Hiroyuki , Wu Fengguang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "J. Bruce Fields" , Neil Brown , Mikulas Patocka , Christoph Hellwig , Theodore Ts'o , linux-ext4@vger.kernel.org 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org