tree 16b383d5c65293575d98ec44264800c0e02807cb
parent 32c1431eea4881a6b17bd7c639315010aeefa452
author Al Viro <viro@ZenIV.linux.org.uk> 1496470809 +0100
committer Al Viro <viro@zeniv.linux.org.uk> 1497523929 -0400

Hang/soft lockup in d_invalidate with simultaneous calls

It's not hard to trigger a bunch of d_invalidate() on the same
dentry in parallel.  They end up fighting each other - any
dentry picked for removal by one will be skipped by the rest
and we'll go for the next iteration through the entire
subtree, even if everything is being skipped.  Morevoer, we
immediately go back to scanning the subtree.  The only thing
we really need is to dissolve all mounts in the subtree and
as soon as we've nothing left to do, we can just unhash the
dentry and bugger off.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>