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

[Al Viro <viro@ZenIV.linux.org.uk>]

On Fri, May 30, 2014 at 08:31:30AM -0700, Linus Torvalds wrote:
> On Fri, May 30, 2014 at 8:21 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > Linus, how would you prefer it to be handled?
> 
> I'll just have to do an rc8. I really hoped to avoid it, because we're
> going on our family vacation when school is out in two weeks, and it
> causes problems for the merge window, but it's not like there is much
> choice - I can't do a 3.15 release with a known regression like that.

Sorry about that... ;-/

> So just send me the pull request, and I'll pull it. I'll probably do
> the "let's increase the x86-64 stack size to 16kB" too, to close
> _that_ issue as well.

OK, here it is:

Fixes for livelocks in shrink_dentry_list() introduced by fixes to shrink
list corruption; the root cause was that trylock of parent's ->d_lock could
be disrupted by d_walk() happening on other CPUs, resulting in
shrink_dentry_list() making no progress *and* the same d_walk() being called
again and again for as long as shrink_dentry_list() doesn't get past that
mess.  Solution is to have shrink_dentry_list() treat that trylock failure not
as "try to do the same thing again", but "lock them in the right order".
Please, pull from
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git for-linus-2

Shortlog:
Al Viro (8):
      lift the "already marked killed" case into shrink_dentry_list()
      split dentry_kill()
      expand dentry_kill(dentry, 0) in shrink_dentry_list()
      shrink_dentry_list(): take parent's ->d_lock earlier
      dealing with the rest of shrink_dentry_list() livelock
      dentry_kill() doesn't need the second argument now
      d_prune_alias(): just lock the parent and call __dentry_kill()
      dcache.c: call ->d_prune() regardless of d_unhashed()

Diffstat:
 fs/dcache.c |  176 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----------------------------------
 1 file changed, 115 insertions(+), 61 deletions(-)