From: Christoph Hellwig Subject: Re: [PATCH 3/3] ext4: Block mmapped writes while the fs is frozen Date: Wed, 18 May 2011 04:07:31 -0400 Message-ID: <20110518080731.GA2759@infradead.org> References: <1305066574-1573-1-git-send-email-jack@suse.cz> <1305066574-1573-4-git-send-email-jack@suse.cz> <20110517151108.GB6653@infradead.org> <20110518075614.GB25632@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ted Tso , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, sandeen@redhat.com To: Jan Kara Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:34449 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754725Ab1ERIHc (ORCPT ); Wed, 18 May 2011 04:07:32 -0400 Content-Disposition: inline In-Reply-To: <20110518075614.GB25632@quack.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, May 18, 2011 at 09:56:14AM +0200, Jan Kara wrote: > __block_page_mkwrite() and return some error value (EAGAIN translating to > VM_FAULT_RETRY would look logical, I just have to think off better error > value for VM_FAULT_NOPAGE). But vfs_check_frozen() cannot be in > __block_page_mkwrite() since ext4 needs to call that with a transaction > started so that would create a deadlock and we need to call > vfs_check_frozen() somewhere so that we don't busyloop. > > I can call vfs_check_frozen() inside block_page_mkwrite() but it would be a > bit surprising difference from __block_page_mkwrite() to me. Not sure what > the cleanest solution would be here... block_page_mkwrite is supposed to be used directly by filesystems and do all the right things. IIRC Eric even mentioned he added vfs_check_frozen to it for RHEL, but forgot to push it upstream.