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From: Marko Rauhamaa <marko.rauhamaa@f-secure.com>
To: Amir Goldstein <amir73il@gmail.com>
CC: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Jan Kara <jack@suse.cz>
Subject: Re: Reproducible, long-standing fanotify+autofs problem
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Date: Thu, 26 Jan 2017 19:47:54 +0200
In-Reply-To: <87inp3rwsy.fsf@drapion.f-secure.com> (Marko Rauhamaa's message
        of "Wed, 25 Jan 2017 17:20:13 +0200")
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Marko Rauhamaa <marko.rauhamaa@f-secure.com>:

> Amir Goldstein <amir73il@gmail.com>:
> I have narrowed the problem down a bit in the kernel. The hanging
> function is "user_path_at":
>
>     user_path_at(filename="/sshome/test/user/", lookup_flags=0x1)
>       called from: fanotify_find_path()
>       called from: fanotify_mark()
>
> And Ctrl-C wakes it up.

I have dug a bit deeper. What hangs is this statement:

    mnt = path->dentry->d_op->d_automount(path);

in:

    follow_automount() // fs/namei.c
      called from: follow_managed()
      called from: walk_component()
      called from: lookup_last()
      called from: path_lookupat()
      called from: filename_lookup()
      called from: user_path_at_empty()
      called from: user_path_at(filename="/sshome/test/user/", lookup_flags=0x1)
      called from: fanotify_find_path() // fs/notify/fanotify_user.c
      called from: fanotify_mark()

And Ctrl-C wakes it up.

The d_automount() method is bound to autofs4_d_automount() in
fs/autofs4/root.c. The hanging statement is:

     wait_event_interruptible(wq->queue, wq->name.name == NULL);

in:

    autofs4_wait() // fs/autofs4/waitq.c
      called from: autofs4_mount_wait() // fs/autofs4/root.c
      called from: autofs4_d_automount()


Marko

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