From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mateusz Guzik Subject: Re: [PATCH 2/2] fs: print a message when freezing/unfreezing filesystems Date: Thu, 15 May 2014 11:42:37 +0200 Message-ID: <20140515094236.GE10637@mguzik.redhat.com> References: <1400005862-3751-1-git-send-email-mguzik@redhat.com> <1400005862-3751-2-git-send-email-mguzik@redhat.com> <20140514215457.GC5421@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Josef Bacik , Jan Kara , Al Viro , Eric Sandeen To: Dave Chinner Return-path: Content-Disposition: inline In-Reply-To: <20140514215457.GC5421@dastard> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, May 15, 2014 at 07:54:57AM +1000, Dave Chinner wrote: > On Tue, May 13, 2014 at 08:31:02PM +0200, Mateusz Guzik wrote: > > This helps hang troubleshooting efforts when only dmesg is available. > > I really don't think that spamming dmesg every time a filesystem is > frozen or thawed is a good idea. This happens a *lot* when systems > are using snapshots, and for the most part nobody cares about > freeze/thaw cycles because they almost always work just fine. > I agree it may get noisy. > I'd think that /proc/self/mounts would be a much better place to > indicate that the fs is frozen. After all, that's where we tell > people whether the filesystem is ro or rw, and frozen is just > a temporary, non-invasive ro state... > Except you can't inspect /proc/self/mounts when the only thing you got is dmesg, so this does not really help my case. That said, I'll try to come up with a different solution. Poorly reported side-effects of frozen I/O are only a part of the real problem which is hung task detector being able to typically report backtraces of "victims" only. I came up with printks becuase these are a cheap way and would help us out in a lot of cases. So general idea is to support providing callbacks when setting tasks to TASK_UNINTERRUPTIBLE which could either tell the user what's up directly or would perform some heuristics. I'll post this in a separate thread later, maybe with PoC. Thanks, -- Mateusz Guzik