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Mon, 6 May 2024 10:42:57 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id v/mzKjG0OGYuHwAAD6G6ig (envelope-from ); Mon, 06 May 2024 10:42:57 +0000 Date: Mon, 6 May 2024 12:42:56 +0200 From: Oscar Salvador To: David Hildenbrand Cc: Baolin Wang , Markus Gothe , "linux-mm@kvack.org" , "akpm@linux-foundation.org" , Zi Yan Subject: Re: get_pageblock_bitmap() sometimes returns a NULL pointer which needs to be properly handled Message-ID: References: <96439935-ce2a-4714-be5d-cdeb8ea0eb41@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <96439935-ce2a-4714-be5d-cdeb8ea0eb41@redhat.com> X-Stat-Signature: mgirgp8pshres13sti5bdfas3szwja8a X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: C03BE40012 X-HE-Tag: 1714992179-870389 X-HE-Meta: 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 gjcxmi8K ZbqgpFQf1GowCbgho7gA8zsnsDNYH2SglnugMP0qeOKS+dPBXA7kPTIy1FHVPy37kpYwFjxyDzgdX7A3Ap5qqOaL5AvVRnE78Ctp4dqmTUDS7DpXfkwp6rCHLsscbysMlcrF7PWKJM1UQDOR/Tu9lRfCiZP16+Ay5AtxIaKZrdZjwqtqeJwBuuMowkuoPiTTiz1WxCtXxK+TSFdHM4Fmhom+JVoAojw1kyycYzIQ6D3FrpPiIEEj0R3YCmV57IoGahXQv6l4g/OxoDsj/J66D+riONCoCN+40po+X X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, May 06, 2024 at 11:54:49AM +0200, David Hildenbrand wrote: > But, could it be that we failing during compaction_alloc() [lr : > compaction_alloc+0x220/0x804] and have an issue during > set_pfnblock_flags_mask() on a page that sits on the isolated freelist? > Similarly, memory hotunplug should not be able to mess up here. But pageblock_flags is something that gets initialized at boot time and never touched again (for already present sections). There are two paths to get it: section_to_usemap(__pfn_to_section(pfn)) or page_zone(page)->pageblock_flags Assuming the we somehow fail in compaction_alloc() and get a bad page or NULL, we should crash before reaching to the point where we ask for pageblock_flags. -- Oscar Salvador SUSE Labs