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Thu, 29 Feb 2024 10:55:39 -0500 X-MC-Unique: QfvGaCbGOI-E_7QxclcMOg-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 11E913C025BB; Thu, 29 Feb 2024 15:55:39 +0000 (UTC) Received: from [10.22.8.117] (unknown [10.22.8.117]) by smtp.corp.redhat.com (Postfix) with ESMTP id ADC5E492BFA; Thu, 29 Feb 2024 15:55:38 +0000 (UTC) Content-Type: multipart/alternative; boundary="------------BE1SzJBSp0pGsxHJVPP3BOnW" Message-ID: Date: Thu, 29 Feb 2024 10:55:38 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/kmemleak: Don't hold kmemleak_lock when calling printk() Content-Language: en-US To: Catalin Marinas Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Audra Mitchell References: <20240228191444.481048-1-longman@redhat.com> From: Waiman Long In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.10 X-Rspamd-Queue-Id: AD86A1C0016 X-Rspam-User: X-Stat-Signature: arewyb6qmca3qufawrbt6yf8mmuw1md8 X-Rspamd-Server: rspam01 X-HE-Tag: 1709222143-43496 X-HE-Meta: U2FsdGVkX18ESkM0gffK8g076W0suvfHAEhyeAeZm9GBX1A2kQ2Hpp3XLhSW1ZxXaX3Q4dCtoZe1TCg9Do2P81w+A/kEQcZ0BRUTRsseWafUYH+AAnH2gIUVoTE5yB5Ag/C1FufhKSA4/sEgvB3MwT+iEawa2Pf0ZiGENxvi0PUODkQQepU5wjkbY5H3oCMBPA7b1yR+xn91BC8EqdCEizs4QtK1+/7PEKZi3iStJBvGanQbyCdpDRxP/oN1nPlgJv5o1WyA2tFuwwYEikHq+SNlhE7YoMH6oLXiy28+KtAJxHpF35WP/XaMMtiz5WOZUeznhribZM44K9xQtTo9UME1IluhC7HCFU4pJYZHXh7RTdyAMrCfYQRGyGYWXqIC3Mm8b9Xu1ONCArUnXk0SoPG3Z4qpyzcuwYo0jNcKN6eDWSr7LmKpII+lvPFwJ3RqsIWxMqmB96Bc0C8VCC515PeA/Mdz/4v4182/SWi7Q2ZiUSGZLx55Wuq5yKN8s3BtOdBPeRwSfwie4MravRC+IYGBxo01kTVsM8vmdAoNH86bYeatwyzSH27ey/IqCT6Q9dNx7mz79dcyxyRfxCJ/N9bvhb+P4cDQFfxFToxyFuLksd/+fQ9nnwXTEOOvuPEIbpTB60efCR6tuschhuF8smcv7r7lV2f4T4fOWbTHTZVjUml4c8hBqzMY+em6VOnU/U+O4PZCDt5Ba3xid23rcHS5Q3VEf9DsDzXUggHMRtAN8HB2tiB438ww+1+xq8clzXB211GzHLnwh5RzPhaWBA51o82wsr/4UaQUTADoQiElnwLynbbMMBCvtCF03DlEZArkDYLZkE7N1SR0/ZAAhYTG3bR23a21eKpVX56VlqB1+HZvqut5JlrKP0lw7qupLD8IY5y1aby67vGVsXbdR1IkY6ISMy4fGU4VhM430A3w5td19snohx3iKlQ5CkBWI3z9rtH/c7DukcHkafn 8pfsCwin PDZijNKz9E9AztUY= 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: List-Subscribe: List-Unsubscribe: This is a multi-part message in MIME format. --------------BE1SzJBSp0pGsxHJVPP3BOnW Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/29/24 10:25, Catalin Marinas wrote: > On Wed, Feb 28, 2024 at 02:14:44PM -0500, Waiman Long wrote: >> When some error conditions happen (like OOM), some kmemleak functions >> call printk() to dump out some useful debugging information while holding >> the kmemleak_lock. This may cause deadlock as the printk() function >> may need to allocate additional memory leading to a create_object() >> call acquiring kmemleak_lock again. >> >> Fix this deadlock issue by making sure that printk() is only called >> after releasing the kmemleak_lock. > I can't say I'm familiar with the printk() code but I always thought it > uses some ring buffers as it can be called from all kind of contexts and > allocation is not guaranteed. > > If printk() ends up taking kmemleak_lock through the slab allocator, I > wonder whether we have bigger problems. The lock order is always > kmemleak_lock -> object->lock but if printk() triggers a callback into > kmemleak, we can also get object->lock -> kmemleak_lock ordering, so > another potential deadlock. object->lock is per object whereas kmemleak_lock is global. When taking object->lock and doing a data dump leading to a call that takes the kmemlock, it is highly unlikely the it will need to take that particular object->lock again. I do agree that lockdep may still warn about it if that happens as all the object->lock's are likely to be treated to be in the same class. I should probably clarify in the change log that the lockdep splat is actually, [ 3991.452558] Chain exists of: [ 3991.452559] console_owner -> &port->lock --> kmemleak_lock So if kmemleak calls printk() acquiring either console_owner or port->lock. It may cause deadlock. Cheers, Longman --------------BE1SzJBSp0pGsxHJVPP3BOnW Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 7bit


On 2/29/24 10:25, Catalin Marinas wrote:
On Wed, Feb 28, 2024 at 02:14:44PM -0500, Waiman Long wrote:

When some error conditions happen (like OOM), some kmemleak functions
call printk() to dump out some useful debugging information while holding
the kmemleak_lock. This may cause deadlock as the printk() function
may need to allocate additional memory leading to a create_object()
call acquiring kmemleak_lock again.

Fix this deadlock issue by making sure that printk() is only called
after releasing the kmemleak_lock.

I can't say I'm familiar with the printk() code but I always thought it
uses some ring buffers as it can be called from all kind of contexts and
allocation is not guaranteed.

If printk() ends up taking kmemleak_lock through the slab allocator, I
wonder whether we have bigger problems. The lock order is always
kmemleak_lock -> object->lock but if printk() triggers a callback into
kmemleak, we can also get object->lock -> kmemleak_lock ordering, so
another potential deadlock.

object->lock is per object whereas kmemleak_lock is global. When taking object->lock and doing a data dump leading to a call that takes the kmemlock, it is highly unlikely the it will need to take that particular object->lock again. I do agree that lockdep may still warn about it if that happens as all the object->lock's are likely to be treated to be in the same class.

I should probably clarify in the change log that the lockdep splat is actually,

[ 3991.452558] Chain exists of: [ 3991.452559] console_owner -> &port->lock --> kmemleak_lock

So if kmemleak calls printk() acquiring either console_owner or port->lock. It may cause deadlock.

Cheers, Longman

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