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Tue, 1 Apr 2025 14:59:47 +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 xZcjL2P/62ejcAAAD6G6ig (envelope-from ); Tue, 01 Apr 2025 14:59:47 +0000 Date: Tue, 1 Apr 2025 16:59:46 +0200 From: Oscar Salvador To: "Vishal Moola (Oracle)" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, muchun.song@linux.dev, Miaohe Lin Subject: Re: [PATCH] mm/compaction: Fix bug in hugetlb handling pathway Message-ID: References: <20250401021025.637333-1-vishal.moola@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250401021025.637333-1-vishal.moola@gmail.com> X-Rspamd-Queue-Id: 3761B1F44E X-Spam-Score: -3.01 X-Rspamd-Action: no action X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[99.99%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; ARC_NA(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_FIVE(0.00)[6]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from]; TAGGED_RCPT(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO X-Spam-Level: On Mon, Mar 31, 2025 at 07:10:24PM -0700, Vishal Moola (Oracle) wrote: > The compaction code doesn't take references on pages until we're certain > we should attempt to handle it. > > In the hugetlb case, isolate_or_dissolve_huge_page() may return -EBUSY > without taking a reference to the folio associated with our pfn. If our > folio's refcount drops to 0, compound_nr() becomes unpredictable, making > low_pfn and nr_scanned unreliable. > The user-visible effect is minimal - this should rarely happen (if ever). So, with compound_order() we either return the real order of the compound page or '0', right? > Fix this by storing the folio statistics earlier on the stack (just like > the THP and Buddy cases). > > Also revert commit 66fe1cf7f581 ("mm: compaction: use helper compound_nr > in isolate_migratepages_block") > to make backporting easier. > > Fixes: 369fa227c219 ("mm: make alloc_contig_range handle free hugetlb pages") > Cc: Miaohe Lin > Cc: Oscar Salvador > Signed-off-by: Vishal Moola (Oracle) Acked-by: Oscar Salvador -- Oscar Salvador SUSE Labs