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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1sjlEk-00000002SwI-1a05; Thu, 29 Aug 2024 19:55:18 +0000 Date: Thu, 29 Aug 2024 20:55:18 +0100 From: Matthew Wilcox To: Luis Chamberlain Cc: Sven Schnelle , "Pankaj Raghav (Samsung)" , brauner@kernel.org, akpm@linux-foundation.org, chandan.babu@oracle.com, linux-fsdevel@vger.kernel.org, djwong@kernel.org, hare@suse.de, gost.dev@samsung.com, linux-xfs@vger.kernel.org, hch@lst.de, david@fromorbit.com, Zi Yan , yang@os.amperecomputing.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, john.g.garry@oracle.com, cl@os.amperecomputing.com, p.raghav@samsung.com, ryan.roberts@arm.com, David Howells , linux-s390@vger.kernel.org Subject: Re: [PATCH v13 04/10] mm: split a folio in minimum folio order chunks Message-ID: References: <20240822135018.1931258-1-kernel@pankajraghav.com> <20240822135018.1931258-5-kernel@pankajraghav.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: DFF3320006 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 8t6hftjqyq1jo4n5d6z6mjtfbgt7fe7t X-HE-Tag: 1724961337-768032 X-HE-Meta: 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 bQjfJ4GQ U5eGplD43DYp1sTnYRUDb6E+6YTR6O0wquaMNsLt7VKIMb9jwk4pJEbS4/N9almuOq9yOq5gNjyWGaHYZME6uxWmeGnhfVVoVrZe1TlD4Mfl5t/nV6TLZVAOfDa4nYcnWQsornUJimaNtINqLjVn4lXX4atgXEkwhd2vdyx3m85Lb6AFCfznCN1lKW3twyHipWu0f9iKJQ6vQUx3IIUcjlgU99h3q18X19hr5yQ2I0GqezgU= 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 Thu, Aug 29, 2024 at 11:46:42AM -0700, Luis Chamberlain wrote: > With vm debugging however I get more information about the issue: > > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: page: refcount:1 mapcount:1 mapping:0000000000000000 index:0x7f589dd7f pfn:0x211d7f > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: memcg:ffff93ba245b8800 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: anon flags: 0x17fffe000020838(uptodate|dirty|lru|owner_2|swapbacked|node=0|zone=2|lastcpupid=0x1ffff) > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: raw: 017fffe000020838 ffffe59008475f88 ffffe59008476008 ffff93ba2abca5b1 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: raw: 00000007f589dd7f 0000000000000000 0000000100000000 ffff93ba245b8800 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: page dumped because: VM_BUG_ON_FOLIO(!folio_test_locked(folio)) > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ------------[ cut here ]------------ > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: kernel BUG at mm/filemap.c:1509! This is in folio_unlock(). We're trying to unlock a folio which isn't locked! > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: Oops: invalid opcode: 0000 [#1] PREEMPT SMP NOPTI > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: CPU: 2 UID: 0 PID: 74 Comm: ksmd Not tainted 6.11.0-rc5-next-20240827 #56 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: RIP: 0010:folio_unlock+0x43/0x50 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: Code: 93 fc ff ff f0 80 30 01 78 06 5b c3 cc cc cc cc 48 89 df 31 f6 5b e9 dc fc ff ff 48 c7 c6 a0 56 49 89 48 89 df e8 2d 03 05 00 <0f> 0b 90 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: RSP: 0018:ffffbb1dc02afe38 EFLAGS: 00010246 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: RAX: 000000000000003f RBX: ffffe59008475fc0 RCX: 0000000000000000 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: RDX: 0000000000000000 RSI: 0000000000000027 RDI: 00000000ffffffff > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000003 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: R10: ffffbb1dc02afce0 R11: ffffffff896c3608 R12: ffffe59008475fc0 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: R13: 0000000000000000 R14: ffffe59008470000 R15: ffffffff89f88060 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: FS: 0000000000000000(0000) GS:ffff93c15fc80000(0000) knlGS:0000000000000000 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: CR2: 0000558e368d9c48 CR3: 000000010ca66004 CR4: 0000000000770ef0 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: PKRU: 55555554 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: Call Trace: > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? die+0x32/0x80 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? do_trap+0xd9/0x100 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? folio_unlock+0x43/0x50 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? do_error_trap+0x6a/0x90 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? folio_unlock+0x43/0x50 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? exc_invalid_op+0x4c/0x60 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? folio_unlock+0x43/0x50 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? asm_exc_invalid_op+0x16/0x20 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? folio_unlock+0x43/0x50 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? folio_unlock+0x43/0x50 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ksm_scan_thread+0x175b/0x1d30 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? __pfx_ksm_scan_thread+0x10/0x10 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: kthread+0xda/0x110 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? __pfx_kthread+0x10/0x10 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ret_from_fork+0x2d/0x50 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ? __pfx_kthread+0x10/0x10 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: ret_from_fork_asm+0x1a/0x30 > Aug 29 18:08:22 nvme-xfs-reflink-4k kernel: [...] > Looking at the KSM code in context ksm_scan_thread+0x175 is mm/ksm.c routine > cmp_and_merge_page() on the split case: > > } else if (split) { > /* > * We are here if we tried to merge two pages and > * failed because they both belonged to the same > * compound page. We will split the page now, but no > * merging will take place. > * We do not want to add the cost of a full lock; if > * the page is locked, it is better to skip it and > * perhaps try again later. > */ > if (!trylock_page(page)) > return; > split_huge_page(page); > unlock_page(page); Obviously the page is locked when we call split_huge_page(). There's an assert inside it. And the lock bit is _supposed_ to be transferred to the head page of the page which is being split. My guess is that this is messed up somehow; we're perhaps transferring the lock bit to the wrong page?