Messages in this thread | | | Date | Wed, 28 May 2014 15:19:37 +0100 | From | Al Viro <> | Subject | Re: fs/dcache.c - BUG: soft lockup - CPU#5 stuck for 22s! [systemd-udevd:1667] |
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On Wed, May 28, 2014 at 04:11:36PM +0300, Mika Westerberg wrote:
> I added this on top of your previus patch and unfortunately the livelock > is still there :-( > > >From the previous log, it looks like udev is doing exactly same operation > (check_submounts_and_drop) on 4 of the CPUs in paraller:
4 threads trying to resolve some pathnames in that subtree for some reason. All of them hitting ->d_revalidate() on the spot - basically, the first invalidated directory...
OK, it's not ->i_lock, it's ->d_lock on parent being grabbed after that on child, while d_walk() keeps taking them in opposite order. Hmm...
In principle we could do the following: * split dentry_kill() into the part that is taking locks and the rest of it. * in case of trylock failure have shrink_dentry_list() do read_seqlock_excl(&rename_lock) (which will stabilize ->d_parent) and take ->d_lock in the right order, drop rename_lock and call __dentry_kill().
AFAICS, that would kill the livelock for good. We still have ->i_lock trylock failures to deal with, but those are less of a problem - d_walk() won't step on ->i_lock at all. I'm going to grab a couple of hours of sleep and try to put together something along those lines...
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