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(p200300cbc70b9c00797830309d9a1aef.dip0.t-ipconnect.de. [2003:cb:c70b:9c00:7978:3030:9d9a:1aef]) by smtp.gmail.com with ESMTPSA id n11-20020a5d4c4b000000b003113ccbf388sm4262884wrt.13.2023.06.21.04.14.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 Jun 2023 04:14:45 -0700 (PDT) Message-ID: <0ed8b92f-583d-7c83-b060-592235627ada@redhat.com> Date: Wed, 21 Jun 2023 13:14:44 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH] mm/page_alloc: Use write_seqlock_irqsave() instead write_seqlock() + local_irq_save(). To: Sebastian Andrzej Siewior , linux-mm@kvack.org Cc: "Luis Claudio R. Goncalves" , Andrew Morton , Mel Gorman , Michal Hocko , Tetsuo Handa , Thomas Gleixner References: <20230621104034.HT6QnNkQ@linutronix.de> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230621104034.HT6QnNkQ@linutronix.de> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 331841C001E X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 7xfdqk1h3y53s4fmoqoup99k66dmiscj X-HE-Tag: 1687346094-166535 X-HE-Meta: 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 lXnSH0dd fNLlXn6On74nF8qgMblWSyF1UXOkzwLyVdpYRV7e3KUeNg/QNCHGNPvsGfNxKIsQgpa/dtjD89wMRMyKoJYLH2ZotcZvD5MzliWzAVUe8SeQ+MjFW5ZGP+1XHL6+JryHGH1xroHbuhiHt/tr9Bb1ORy6d3tL31e/StFVlIL15V+pO0lSjMW7p1cJUY8cNRFIxt6Ye10BYpgGrjbC4kjM9tOzOh3OtugFl4rIWF6e99CbT+YP7tG6mlICsl9sSz8BSCQaM7KWQgcPBbdL589OeULa4lBEsKR9MVR41uF92n0AQPviA8iFgFvM7P4rW7DzUVYQ7GrnU623BSDZWBz0JeD3kinl8aZQQf/SxmucruEdxjiHjUYC++zMrc/mh2mZ9a3//HkS/jmPbT3upbQnoGKkKi31WJ8g2lK8yvZow9Z3pw4iHnGpp/HVbb+p6R+8i+kBeRbMs9pP47o0= 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 21.06.23 12:40, Sebastian Andrzej Siewior wrote: > __build_all_zonelists() acquires zonelist_update_seq by first disabling > interrupts via local_irq_save() and then acquiring the seqlock with > write_seqlock(). This is troublesome and leads to problems on > PREEMPT_RT because the inner spinlock_t is now acquired with disabled > interrupts. > The API provides write_seqlock_irqsave() which does the right thing in > one step. > printk_deferred_enter() has to be invoked in non-migrate-able context to > ensure that deferred printing is enabled and disabled on the same CPU. > This is the case after zonelist_update_seq has been acquired. > > Acquire zonelist_update_seq with write_seqlock_irqsave() and then defer > printk output. > > Fixes: 1007843a91909 ("mm/page_alloc: fix potential deadlock on zonelist_update_seq seqlock") > Signed-off-by: Sebastian Andrzej Siewior > --- > mm/page_alloc.c | 11 ++++------- > 1 file changed, 4 insertions(+), 7 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 47421bedc12b7..99b7e7d09c5c0 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5808,11 +5808,10 @@ static void __build_all_zonelists(void *data) > unsigned long flags; > > /* > - * Explicitly disable this CPU's interrupts before taking seqlock > - * to prevent any IRQ handler from calling into the page allocator > - * (e.g. GFP_ATOMIC) that could hit zonelist_iter_begin and livelock. > + * The zonelist_update_seq must be acquired with irqsave because the > + * reader can be invoked from IRQ with GFP_ATOMIC. > */ > - local_irq_save(flags); > + write_seqlock_irqsave(&zonelist_update_seq, flags); > /* > * Explicitly disable this CPU's synchronous printk() before taking > * seqlock to prevent any printk() from trying to hold port->lock, for > @@ -5820,7 +5819,6 @@ static void __build_all_zonelists(void *data) > * calling kmalloc(GFP_ATOMIC | __GFP_NOWARN) with port->lock held. > */ > printk_deferred_enter(); > - write_seqlock(&zonelist_update_seq); > > #ifdef CONFIG_NUMA > memset(node_load, 0, sizeof(node_load)); > @@ -5857,9 +5855,8 @@ static void __build_all_zonelists(void *data) > #endif > } > > - write_sequnlock(&zonelist_update_seq); > printk_deferred_exit(); > - local_irq_restore(flags); > + write_sequnlock_irqrestore(&zonelist_update_seq, flags); > } > > static noinline void __init Reviewed-by: David Hildenbrand -- Cheers, David / dhildenb