linux-kernel - Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion

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Message-ID: <20170915221238.js6elr5jmj4mgt67@thunk.org>
Date:   Fri, 15 Sep 2017 18:12:38 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Al Viro <viro@...IV.linux.org.uk>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount
 completion

On Fri, Sep 15, 2017 at 11:44:33AM -0700, Jaegeuk Kim wrote:
> 
> So, I digged it in more detail, and found, in drivers/android/binder.c [1],
> - binder_ioctl()
>  - create a kernel thread
>  - zombie_cleanup_check()
>   - binder_defer_work()
>     - queue_work(..., &binder_deferred_work);
> 
> - binder_deferred_func()
>  - binder_clear_zombies()
>   - binder_proc_clear_zombies()
>    - put_files_struct()
>     - close_files()
>      - filp_close()
>       - fput()
> 
> It seems binder holds some proc files.

If binder was holding some files open, then umount should have failed
with EBUSY, no?

Does Android use mount namespaces at all?

					- Ted