Dmitry, can you assign VM resources for a git tree for this bug? This bug wants to fight against https://github.com/google/syzkaller/blob/master/docs/syzbot.md#no-custom-patches ... On 2018/06/01 1:56, Jens Axboe wrote: > On 5/31/18 7:42 AM, Jan Kara wrote: >> On Thu 31-05-18 22:19:44, Tetsuo Handa wrote: >>> On 2018/05/31 20:42, Jan Kara wrote: >>>> On Thu 31-05-18 01:00:08, Tetsuo Handa wrote: >>>>> So, we have no idea what is happening... >>>>> Then, what about starting from temporary debug printk() patch shown below? >>>>> >>>>> >From 4f70f72ad3c9ae6ce1678024ef740aca4958e5b0 Mon Sep 17 00:00:00 2001 >>>>> From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> >>>>> Date: Wed, 30 May 2018 09:57:10 +0900 >>>>> Subject: [PATCH] bdi: Add temporary config for debugging wb_workfn() versus >>>>> bdi_unregister() race bug. >>>>> >>>>> syzbot is hitting NULL pointer dereference at wb_workfn() [1]. But due to >>>>> limitations that syzbot cannot find reproducer for this bug (frequency is >>>>> once or twice per a day) nor we can't capture vmcore in the environment >>>>> which syzbot is using, for now we need to rely on printk() debugging. >>>>> >>>>> [1] https://syzkaller.appspot.com/bug?id=e0818ccb7e46190b3f1038b0c794299208ed4206 >>>>> >>>>> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> >>>> >>>> Hum a bit ugly solution but if others are fine with this, I can live with >>>> it for a while as well. Or would it be possible for syzkaller to just test >>>> some git tree where this patch is included? Then we would not even have to >>>> have the extra config option... >>> >>> If syzbot can reproduce this bug that way. While it is possible to add/remove >>> git trees syzbot tests, frequently adding/removing trees is bothering. >>> >>> syzbot can enable extra config option. Maybe the config name should be >>> something like CONFIG_DEBUG_FOR_SYZBOT rather than individual topic. >>> >>> I think that syzbot is using many VM instances. I don't know how many >>> instances will be needed for reproducing this bug within reasonable period. >>> More git trees syzbot tests, (I assume that) longer period will be needed >>> for reproducing this bug. The most reliable way is to use the shared part >>> of all trees (i.e. linux.git). >> >> I understand this, I'd be just a bit reluctant to merge temporary debug >> patches like this to Linus' tree only to revert them later just because >> syzkaller... What do others think? > > I guess I don't understand why having it in Linus's tree would make > a difference to syzkaller? > > If there is a compelling reason why that absolutely has to be done, > I don't think it should be accompanied by a special Kconfig option > for it. It should just be on unconditionally, with the intent to > remove it before release. >
