From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E157EC433E0 for ; Thu, 16 Jul 2020 15:31:11 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A14832065F for ; Thu, 16 Jul 2020 15:31:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A14832065F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=I-love.SAKURA.ne.jp Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4664A8D0021; Thu, 16 Jul 2020 11:31:11 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 417878D0016; Thu, 16 Jul 2020 11:31:11 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3549F8D0021; Thu, 16 Jul 2020 11:31:11 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0159.hostedemail.com [216.40.44.159]) by kanga.kvack.org (Postfix) with ESMTP id 2175C8D0016 for ; Thu, 16 Jul 2020 11:31:11 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 8CE0C2DFD for ; Thu, 16 Jul 2020 15:31:10 +0000 (UTC) X-FDA: 77044327500.28.bead75_0b0f5c426f03 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin28.hostedemail.com (Postfix) with ESMTP id 9BF736D93 for ; Thu, 16 Jul 2020 15:31:02 +0000 (UTC) X-HE-Tag: bead75_0b0f5c426f03 X-Filterd-Recvd-Size: 2746 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Thu, 16 Jul 2020 15:31:01 +0000 (UTC) Received: from fsav102.sakura.ne.jp (fsav102.sakura.ne.jp [27.133.134.229]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 06GFUgOo080175; Fri, 17 Jul 2020 00:30:42 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav102.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav102.sakura.ne.jp); Fri, 17 Jul 2020 00:30:42 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav102.sakura.ne.jp) Received: from localhost.localdomain (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 06GFUbtS079989 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Fri, 17 Jul 2020 00:30:42 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) From: Tetsuo Handa To: Andrew Morton Cc: linux-mm , Tetsuo Handa Subject: [PATCH] mm: Warn mmput() from memory reclaim context. Date: Fri, 17 Jul 2020 00:30:34 +0900 Message-Id: <20200716153034.4935-1-penguin-kernel@I-love.SAKURA.ne.jp> X-Mailer: git-send-email 2.18.4 X-Rspamd-Queue-Id: 9BF736D93 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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: syzbot is reporting that mmput() from shrinker function has a risk of deadlock [1], for delayed_uprobe_add() from update_ref_ctr() calls kzalloc(GFP_KERNEL) with delayed_uprobe_lock held, and uprobe_clear_state() from __mmput() also holds delayed_uprobe_lock. However, it took 18 months to hit this race for the third time, for mmput() invokes __mmput() only when ->mm_users dropped to 0. If we always warn like might_sleep(), we can detect the possibility of deadlock more easier. For now, I inlined the check under CONFIG_PROVE_LOCKING. If we find more locations, we could introduce a macro like might_sleep(). [1] https://syzkaller.appspot.com/bug?id=bc9e7303f537c41b2b0cc2dfcea3fc42964c2d45 Signed-off-by: Tetsuo Handa --- kernel/fork.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index efc5493203ae..8717ce50ff0d 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1109,6 +1109,10 @@ static inline void __mmput(struct mm_struct *mm) void mmput(struct mm_struct *mm) { might_sleep(); +#ifdef CONFIG_PROVE_LOCKING + /* Calling mmput() from shrinker context can deadlock. */ + WARN_ON(current->flags & PF_MEMALLOC); +#endif if (atomic_dec_and_test(&mm->mm_users)) __mmput(mm); -- 2.18.4