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bh=06YfdiGd9c/su5IVzBCTSzjJnzm0BSgC6bzhGK9XIL4=; b=e8+o0xonZ5FOuEkkGBl096T30uSKs0+4bTeuZgjcERFn1zVy3Vye9X8WQhybU67YPyqef9 +N3SHkmaq7S8hVmlhhFGytIP7r26iKUiYMqd3+/yeMJEnjV0dWW0872rzwiAdqRBQQbQ1V Xsc7aoMuQ5+2N84edDDQP/ME6xCBXtU= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id C0A2A13920; Tue, 4 Apr 2023 07:54:18 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id 2wpcLqrXK2TOfgAAMHmgww (envelope-from ); Tue, 04 Apr 2023 07:54:18 +0000 Date: Tue, 4 Apr 2023 09:54:18 +0200 From: Michal Hocko To: Tetsuo Handa Cc: Petr Mladek , Patrick Daly , Mel Gorman , David Hildenbrand , Andrew Morton , Sergey Senozhatsky , Steven Rostedt , John Ogness , syzkaller-bugs@googlegroups.com, Ilpo =?iso-8859-1?Q?J=E4rvinen?= , syzbot , linux-mm Subject: Re: [PATCH] mm/page_alloc: fix potential deadlock on zonelist_update_seq seqlock Message-ID: References: <000000000000b21f0a05e9ec310d@google.com> <78ff6e70-e986-1fcb-eafb-3edd5f2bceae@I-love.SAKURA.ne.jp> <6266b161-e4c3-7d65-6590-da6cc04d93ec@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6266b161-e4c3-7d65-6590-da6cc04d93ec@I-love.SAKURA.ne.jp> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 4065EC000B X-Stat-Signature: g6cugwupoqe5b4camuk8pq7f8xpzd55r X-HE-Tag: 1680594860-852861 X-HE-Meta: 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 0UMQZ/1u 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 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 Tue 04-04-23 09:37:25, Tetsuo Handa wrote: > syzbot is reporting circular locking dependency which involves > zonelist_update_seq seqlock [1], for this lock is checked by memory > allocation requests which do not need to be retried. > > We somehow need to prevent __alloc_pages_slowpath() from checking > this lock. Since Petr Mladek thinks that __build_all_zonelists() can > become a candidate for deferring printk() [2], let's make sure that > current CPU/thread won't reach __alloc_pages_slowpath() while this lock > is in use. I agree with Petr that the lockdep splat and the lockup explanation should be part of the changelog. Just reuse what you had in previous email. > Reported-by: syzbot > Link: https://syzkaller.appspot.com/bug?extid=223c7461c58c58a4cb10 [1] > Fixes: 3d36424b3b58 ("mm/page_alloc: fix race condition between build_all_zonelists and page allocation") > Link: https://lkml.kernel.org/r/ZCrs+1cDqPWTDFNM@alley [2] > Signed-off-by: Tetsuo Handa > Cc: Michal Hocko > Cc: Petr Mladek > --- > mm/page_alloc.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 7136c36c5d01..64fa77b8d24a 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -6632,7 +6632,21 @@ static void __build_all_zonelists(void *data) > int nid; > int __maybe_unused cpu; > pg_data_t *self = data; > + unsigned long flags; > > + /* > + * Since __alloc_pages_slowpath() spins if zonelist_update_seq.seqcount > + * is odd, any memory allocation while zonelist_update_seq.seqcount is > + * odd have to be avoided. > + * > + * Explicitly disable local irqs in order to avoid calling > + * kmalloc(GFP_ATOMIC) from e.g. timer interrupt handler. > + * Also, explicitly prevent printk() from synchronously waiting for > + * port->lock because tty_insert_flip_string_and_push_buffer() might > + * call kmalloc(GFP_ATOMIC | __GFP_NOWARN) while holding port->lock. This explanation of local_irq_save just doesn't make any sense. You do not prevent any other cpu from entering the IRQ and doing the same thing. If the sole purpose of local_irq_save is to conform printk_deferred_enter then state that instead. Although it seems that Petr believes that preempt_disable should be sufficient and then it would be preferred as well. This would require update to the comment for printk_deferred_enter though. Thanks! > + */ > + local_irq_save(flags); > + printk_deferred_enter(); > write_seqlock(&zonelist_update_seq); > > #ifdef CONFIG_NUMA > @@ -6671,6 +6685,8 @@ static void __build_all_zonelists(void *data) > } > > write_sequnlock(&zonelist_update_seq); > + printk_deferred_exit(); > + local_irq_restore(flags); > } > > static noinline void __init > -- > 2.34.1 -- Michal Hocko SUSE Labs