linux-kernel - Re: Umount failing due to a file leak on 3.18 Android

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Date:	Wed, 20 Apr 2016 14:55:58 +0900
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Nikhilesh Reddy <reddyn@...eaurora.org>
Cc:	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Umount failing due to a file leak on 3.18 Android

On Tue, Apr 19, 2016 at 06:26:27PM -0700, Nikhilesh Reddy wrote:
> Hi
> 
> I am looking into a bug that results in umount failures ( since there is a mount ref from the leaked file that is never freed on the mount )
> 
> The issue seems to be a result of the following callstack
> 
>     39.958104:   <6> Call trace:
>     39.958108:   <2> [<ffffffc0001baa58>] fput+0x1e0/0x1f8
>     39.958113:   <2> [<ffffffc0001b6ce8>] filp_close+0xa0/0xb8
>     39.958119:   <2> [<ffffffc0001d3ca8>] put_files_struct+0x88/0xf0
>     39.958123:   <2> [<ffffffc000973c40>] binder_deferred_func+0x6a8/0x704
>     39.958129:   <2> [<ffffffc0000ba32c>] process_one_work+0x238/0x3f0
>     39.958133:   <2> [<ffffffc0000bb160>] worker_thread+0x2f8/0x418
> 
> What seems to occur is that once in a while a file ( say a.txt) is fput in the above stack 
> right as the task is being killed
> 
> And then we see that the  fput schedules a delayed_fput_work on this file
> 
> But when the function delayed_fput() is actually run :
> 	the file that was put i.e this a.txt is not in the delayed_fput_list
> 
> Any chance you can help me get to the bottom of this leak?
> I dont understand why the delayed_fput_list is missing the file.

3.18 is very old, can you duplicate this on 4.5 or newer?

thanks,

greg k-h