linux-ext4 - Re: [Bug 216529] [fstests generic/048] BUG: Kernel NULL pointer dereference at 0x00000069, filemap_release

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Message-ID: <YzM7nhdg8mLhkgSB@mit.edu>
Date:   Tue, 27 Sep 2022 14:06:22 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     bugzilla-daemon@...nel.org
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [Bug 216529] [fstests generic/048] BUG: Kernel NULL pointer
 dereference at 0x00000069, filemap_release_folio+0x88/0xb0

On Tue, Sep 27, 2022 at 12:47:02AM +0000, bugzilla-daemon@...nel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=216529
> 
> Yes, it's reproducible for me, I just reproduced it again on another ppc64le
> (P8) machine [1]. But it's not easy to reproduce by running generic/048 (maybe
> there's a better way to reproduce it).

Can you give a rough percentage of how often it reproduces?  e.g.,
does it reproduces 10% of the time?  50% of the time?  2-3 times after
100 tries, so 2-3%?  etc.  If it reproduces but rarely, it'll be a lot
harder to try to bisect.

Something perhaps to try is to enable KASAN, since both stack traces
seem to involve a null pointer derference while trying to free
buffers.   Maybe that will give us some hints towards the cause....

Thanks,

						- Ted