From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Tue, 12 Dec 2006 02:41:43 -0800 (PST) Received: from smtp.osdl.org (smtp.osdl.org [65.172.181.25]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with ESMTP id kBCAfVqw029406 for ; Tue, 12 Dec 2006 02:41:33 -0800 Date: Tue, 12 Dec 2006 02:40:27 -0800 From: Andrew Morton Subject: Re: [PATCH] incorrect error handling inside generic_file_direct_write Message-Id: <20061212024027.6c2a79d3.akpm@osdl.org> In-Reply-To: <87psapz1zr.fsf@sw.ru> References: <87k60y1rq4.fsf@sw.ru> <20061211124052.144e69a0.akpm@osdl.org> <87bqm9tie3.fsf@sw.ru> <20061212015232.eacfbb46.akpm@osdl.org> <87psapz1zr.fsf@sw.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: Dmitriy Monakhov Cc: Dmitriy Monakhov , linux-kernel@vger.kernel.org, Linux Memory Management , devel@openvz.org, xfs@oss.sgi.com On Tue, 12 Dec 2006 16:18:32 +0300 Dmitriy Monakhov wrote: > >> but according to filemaps locking rules: mm/filemap.c:77 > >> .. > >> * ->i_mutex (generic_file_buffered_write) > >> * ->mmap_sem (fault_in_pages_readable->do_page_fault) > >> .. > >> I'm confused a litle bit, where is the truth? > > > > xfs_write() calls generic_file_direct_write() without taking i_mutex for > > O_DIRECT writes. > Yes, but my quastion is about __generic_file_aio_write_nolock(). > As i understand _nolock sufix means that i_mutex was already locked > by caller, am i right ? Nope. It just means that __generic_file_aio_write_nolock() doesn't take the lock. We don't assume or require that the caller took it. For example the raw driver calls generic_file_aio_write_nolock() without taking i_mutex. Raw isn't relevant to the problem (although ocfs2 might be). But we cannot assume that all callers have taken i_mutex, I think. I guess we can make that a rule (document it, add BUG_ON(!mutex_is_locked(..)) if it isn't a blockdev) if needs be. After really checking that this matches reality for all callers. It's important, too - if we have an unprotected i_size_write() then the seqlock can get out of sync due to a race and then i_size_read() locks up the kernel.