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Sat, 13 May 2023 08:13:27 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: <61d7ac52-3352-b7cd-8908-890a29a007d9@I-love.SAKURA.ne.jp> Date: Sat, 13 May 2023 08:13:27 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.10.1 Subject: Re: [PATCH] debugobject: don't wake up kswapd from fill_pool() Content-Language: en-US To: Thomas Gleixner , Andrew Morton Cc: syzbot , syzkaller-bugs@googlegroups.com, Ingo Molnar , linux-kernel@vger.kernel.org, linux-mm References: <000000000000008ddb05fb5e2576@google.com> <6577e1fa-b6ee-f2be-2414-a2b51b1c5e30@I-love.SAKURA.ne.jp> <20230511204458.819f9009d2ef8b46cc163191@linux-foundation.org> <87v8gxbthf.ffs@tglx> <39c79d27-73ea-06a8-62fe-2b64d0fd8db5@I-love.SAKURA.ne.jp> <87bkipbeyr.ffs@tglx> From: Tetsuo Handa In-Reply-To: <87bkipbeyr.ffs@tglx> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: fn6rm44urxeitjgs1i7wk9ph835mb66t X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 7155314001B X-HE-Tag: 1683933304-555698 X-HE-Meta: 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 6VH0CYig kll5ZSRFA4/UZGpm3s+kQA1uFPgQ0+qRBfxUWPGxb18/RqntBIHEjeaDN63/xSNbdITZsNhOT1NNMPGxtrKGgJE8ynz2A11w+xoZyDsQo6SiRkpZj4er+Ycx30dujwndFL9bZy45yZhcfBfzb9IjnydSK7RJz+R/T3/xpB8LiPr3n1gPgH8njxFaOyNLVVKutg+JHNb1doPkh4MaeCR6Bsx32Zg9rJ+e1clmIULWqlbbY3OH/ZkUtuvs8H4OYOP09eeqQmgH2FeuB/3sJT+ESC5Vm+uSbOzWauS9N5ZADrfKEFiKsgfvSJSrGAhpF+6AHI65vTdcQ6FRs0NIn5OOArnHk0vMEfDDMx2lECJD2O8YLPxyhBhswefCqPUH7J//ILjStCaV81G3ck0m132vQ3zTw8aVjvew92Hog0gudnLykjqE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2023/05/13 3:07, Thomas Gleixner wrote: > On Fri, May 12 2023 at 22:09, Tetsuo Handa wrote: >> On 2023/05/12 21:54, Thomas Gleixner wrote: >>> On Fri, May 12 2023 at 19:57, Tetsuo Handa wrote: >>>> On 2023/05/12 12:44, Andrew Morton wrote: >>>>> On Thu, 11 May 2023 22:47:32 +0900 Tetsuo Handa wrote: >>>>> >>>>>> syzbot is reporting lockdep warning in fill_pool(), for GFP_ATOMIC is >>>>>> (__GFP_HIGH | __GFP_KSWAPD_RECLAIM) which wakes up kswapd. >>>>>> Since fill_pool() might be called with arbitrary locks held, >>>>>> fill_pool() should not assume that holding pgdat->kswapd_wait is safe. >>> >>> https://lore.kernel.org/lkml/871qjldbes.ffs@tglx/ >> >> .config says IS_ENABLED(CONFIG_PREEMPT_RT) == false, and lockdep says about >> base->lock => pgdat->kswapd_wait => p->pi_lock => rq->__lock => base->lock >> dependency but does not say about db->lock. >> >> How can your patch fix this problem? > > It's described in the changelog, no? I can't find a proof that lookup_object() never returns NULL when debug_object_activate() is called. > > The main change is to make the refill invocation conditional when the > lookup fails. That's how that code has been from day one. Making refill conditional helps reducing frequency of doing allocations. I want a proof that allocations never happens in the worst scenario. Are you saying that some debugobject function other than debug_object_activate() guarantees that memory for that object was already allocated before debug_object_activate() is called for the first time for that object, _and_ such debugobject function is called without locks held? > > The patch which closed the race recently wreckaged those refill > oportunities and the fix for that introduced this problem. > > Thanks, > > tglx