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Date:   Tue, 26 Mar 2019 10:30:53 +0900
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     stable@vger.kernel.org, Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>, Waiman Long <longman@redhat.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [BACKPORT 4.4.y 20/25] Hang/soft lockup in d_invalidate with
 simultaneous calls
Message-ID: <20190326013053.GA21198@kroah.com>
References: <20190322154425.3852517-1-arnd@arndb.de>
 <20190322154425.3852517-21-arnd@arndb.de>
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On Fri, Mar 22, 2019 at 04:44:11PM +0100, Arnd Bergmann wrote:
> From: Al Viro <viro@ZenIV.linux.org.uk>
> 
> 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>
> (cherry picked from commit 81be24d263dbeddaba35827036d6f6787a59c2c3)
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  fs/dcache.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)

Also added to 4.9.y