From: Christoph Hellwig Subject: Re: [PATCH 3/3] ext4: Block mmapped writes while the fs is frozen Date: Tue, 17 May 2011 11:11:08 -0400 Message-ID: <20110517151108.GB6653@infradead.org> References: <1305066574-1573-1-git-send-email-jack@suse.cz> <1305066574-1573-4-git-send-email-jack@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 To: Jan Kara Return-path: Content-Disposition: inline In-Reply-To: <1305066574-1573-4-git-send-email-jack@suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Wed, May 11, 2011 at 12:29:34AM +0200, Jan Kara wrote: > We should not allow file modification via mmap while the filesystem is > frozen. So block in ext4_page_mkwrite() while the filesystem is frozen. > > We have to check for frozen filesystem with the page marked dirty and under > page lock with which we then return from ext4_page_mkwrite(). Only that way we > cannot race with writeback done by freezing code - either we mark the page > dirty after the writeback has started, see freezing in progress and block, or > writeback will wait for our page lock which is released only when the fault is > done and then writeback will writeout and writeprotect the page again. This really should be done in (__)block_page_mkwrite. I'd also return VM_FAULT_RETRY instead of retrying inside the block_mkwrite handler in case you hit the race.