bug#43344: "basic" system tests fail (and all the other ones) on guix master

[Mark H Weaver]

Leo Famulari <leo@famulari.name> writes:

> On Wed, Sep 16, 2020 at 04:52:45PM +0200, Danny Milosavljevic wrote:
>> commit 692d0626557451c4b557397f20b7394b612d0289
>> Author: Christoph Hellwig <hch@lst.de>
>> Date:   Tue Sep 1 11:59:41 2020 +0200
>> 
>>     block: fix locking in bdev_del_partition
>>     
>>     [ Upstream commit 08fc1ab6d748ab1a690fd483f41e2938984ce353 ]
>>     
>>     We need to hold the whole device bd_mutex to protect against
>>     other thread concurrently deleting out partition before we get
>>     to it, and thus causing a use after free.
>>     
>>     Fixes: cddae808aeb7 ("block: pass a hd_struct to delete_partition")
>>     Reported-by: syzbot+6448f3c229bc52b82f69@syzkaller.appspotmail.com
>>     Signed-off-by: Christoph Hellwig <hch@lst.de>
>>     Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>     Signed-off-by: Sasha Levin <sashal@kernel.org>
>> 
>> ?
>
> Do you think that's the faulty commit? I won't have time to test it
> today.

Looks like a good bet to me.  Many thanks to Leo for testing 5.8.9, and
to Danny for identifying the likely culprit.

Next, it probably makes sense to test 5.8.9 with the above commit
reverted.  Would someone like to try it?  If that works, we can avoid
the bisection, resume kernel updates, and revert this change across all
of our kernels until a better solution is found.

        Mark