Re: fs/dcache.c - BUG: soft lockup - CPU#5 stuck for 22s! [systemd-udevd:1667]

[Mika Westerberg]

On Thu, May 29, 2014 at 01:51:07PM +0300, Mika Westerberg wrote:
> On Thu, May 29, 2014 at 06:34:44AM +0100, Al Viro wrote:
> > On Thu, May 29, 2014 at 04:52:33AM +0100, Al Viro wrote:
> > > On Thu, May 29, 2014 at 04:11:49AM +0100, Al Viro wrote:
> > > > On Wed, May 28, 2014 at 07:39:54PM +0100, Al Viro wrote:
> > > > 
> > > > > OK, the warnings about averting your eyes very much apply; the thing below
> > > > > definitely needs more massage before it becomes acceptable (and no, it's
> > > > > not a single commit; I'm not that insane), but it changes behaviour in the
> > > > > way described above.  Could you check if the livelock persists with it?
> > > > > No trace-generating code in there, so the logs should be compact enough...
> > > > 
> > > > Here's an updated patch, hopefully slightly less vomit-inducing.  Should
> > > > give the same behaviour as the previous one...  Again, it's a cumulative
> > > > diff - I'm still massaging the splitup here.
> > > 
> > > BTW, it still leaves the "proceed to parent" case in shrink_dentry_list();
> > > in theory, it's also vulnerable to the same livelock.  Can be dealt pretty
> > > much the same way; I'd rather leave that one for right after -final, though,
> > > if the already posted variant turns out to be sufficient...
> > 
> > ... which is (presumably) dealt with the incremental I'd just sent to Linus;
> > seeing what kind of dumb mistakes I'm making, I'd better call it quits for
> > tonight - it's 1:30am here and I didn't have anywhere near enough sleep
> > yesterday.  I'd appeciate if you could test the patch immediately
> > upthread (from Message-ID: <20140529031149.GE18016@xxxxxxxxxxxxxxxxxx>)
> > and see if it helps.  There's an incremental on top of it (from
> > Message-ID: <20140529052621.GH18016@xxxxxxxxxxxxxxxxxx>) that might or
> > might not be a good idea.
> 
> Thanks for the patch.
> 
> I tested patch <20140529031149.GE18016@xxxxxxxxxxxxxxxxxx> and it seems
> to improve things. After first plug/unplug I can see similar behaviour
> but after a while it recovered. I did several iterations of plug/unplug
> afterwards and didn't see the livelock to trigger.
> 
> dmesg is attached.
> 
> I'm going to try your incremental patch now.

With your both patches applied the problem is gone :-)

I did 20 plug/unplugs, rebooted the machine and another 20 plug/unplugs
and didn't see the livelock at once.

Thanks a lot!
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