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

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Message-ID: <5716DAC3.4070404@codeaurora.org>
Date:	Tue, 19 Apr 2016 18:26:27 -0700
From:	Nikhilesh Reddy <reddyn@...eaurora.org>
To:	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Greg KH <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Umount failing due to a file leak on 3.18 Android

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.

Is there some sort of race condition?

-- 
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.