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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sYBGf-0000000CoVl-38SQ; Sun, 28 Jul 2024 21:17:25 +0000 Date: Sun, 28 Jul 2024 22:17:25 +0100 From: Matthew Wilcox To: Andrew Morton Cc: Gao Xiang , Huang Ying , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/migrate: fix deadlock in migrate_pages_batch() on large folios Message-ID: References: <20240728154913.4023977-1-hsiangkao@linux.alibaba.com> <20240728125005.c1171fa2d1beb6c1fe867d48@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240728125005.c1171fa2d1beb6c1fe867d48@linux-foundation.org> X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: B74A31C000F X-Stat-Signature: gcdysyeb6fkapd3ydiz4mjciss77d3gr X-HE-Tag: 1722201450-749440 X-HE-Meta: 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 Jid8jq7J zP1NL31WcnKrv8f7QAAs2+dzjF5oFE8u0WYMZyDDdcBnu42bl66pL3KfXVZvlEYFBw+1XpT/b+W+Nb3pfsnnNMbS+OMQ94pGSA7gn58Vo2Zxk7KwkQ4FjXE/NQHf5nC2i+OrbU/9ZXKyadpwD/J69CKCcbUuKeoJTl8peNXaT206LlyiWm6zMcNwAizRBLG3hO3kwArvBPZvmR8LDjxGqjkptMP4HxBCWYo+jw9/ixnhdEaxVA81MUynj+xWa+I/Mwul3AmZt3rbmat51cAf6mF6/dA== 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: On Sun, Jul 28, 2024 at 12:50:05PM -0700, Andrew Morton wrote: > On Sun, 28 Jul 2024 23:49:13 +0800 Gao Xiang wrote: > > Currently, migrate_pages_batch() can lock multiple locked folios > > with an arbitrary order. Although folio_trylock() is used to avoid > > deadlock as commit 2ef7dbb26990 ("migrate_pages: try migrate in batch > > asynchronously firstly") mentioned, it seems try_split_folio() is > > still missing. > > Am I correct in believing that folio_lock() doesn't have lockdep coverage? Yes. It can't; it is taken in process context and released by whatever context the read completion happens in (could be hard/soft irq, could be a workqueue, could be J. Random kthread, depending on the device driver) So it doesn't match the lockdep model at all. > > It was found by compaction stress test when I explicitly enable EROFS > > compressed files to use large folios, which case I cannot reproduce with > > the same workload if large folio support is off (current mainline). > > Typically, filesystem reads (with locked file-backed folios) could use > > another bdev/meta inode to load some other I/Os (e.g. inode extent > > metadata or caching compressed data), so the locking order will be: > > Which kernels need fixing. Do we expect that any code paths in 6.10 or > earlier are vulnerable to this? I would suggest it goes back to the introduction of large folios, but that's just a gut feeling based on absolutely no reading of code or inspection of git history.