From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 29 Nov 2016 11:43:50 -0500 From: Tejun Heo To: Jan Kara Cc: Wei Fang , akpm@linux-foundation.org, hannes@cmpxchg.org, hch@infradead.org, linux-mm@kvack.org, stable@vger.kernel.org, Jens Axboe Subject: Re: [PATCH] mm: Fix a NULL dereference crash while accessing bdev->bd_disk Message-ID: <20161129164350.GC19454@htj.duckdns.org> References: <1480125982-8497-1-git-send-email-fangwei1@huawei.com> <20161128100718.GD2590@quack2.suse.cz> <20161128155718.GB7806@htj.duckdns.org> <20161129093035.GC7550@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161129093035.GC7550@quack2.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: Hello, Jan. On Tue, Nov 29, 2016 at 10:30:35AM +0100, Jan Kara wrote: > > It's kinda weird that sync() is ends up accessing bdev's without any > > synchronization. Can't we just make iterate_bdevs() grab bd_mutex and > > verify bd_disk isn't NULL before calling into the callback? > > This reminded me I've already seen something like this and indeed I've > already had a very similar discussion in March - > https://patchwork.kernel.org/patch/8556941/ lol > Holding bd_mutex in iterate_devs() works but still nothing protects from > flusher thread just walking across the block device inode and trying to > write it which would result in the very same oops. Ah, right. We aren't implementing either sever or refcnted draining semantics properly. I wonder whether we'd be able to retire the inode synchronously during blkdev_put. Thanks. -- tejun -- 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/ . Don't email: email@kvack.org