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([2405:201:682f:389d:60a2:fbdd:54e6:8eb3]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29034f961c5sm30527265ad.129.2025.10.09.07.29.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Oct 2025 07:29:22 -0700 (PDT) From: Deepanshu Kartikey To: joseph.qi@linux.alibaba.com, mark@fasheh.com, jlbec@evilplan.org Cc: ocfs2-devel@lists.linux.dev, linux-kernel@vger.kernel.org, syzbot+6fdd8fa3380730a4b22c@syzkaller.appspotmail.com Subject: Re: [PATCH] ocfs2: fix stale extent map cache during COW operations Date: Thu, 9 Oct 2025 19:59:16 +0530 Message-ID: <20251009142917.517229-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hi Joseph, Thank you for the review. You are absolutely right - the cache clearing at the end of ocfs2_refcount_cow_hunk() should handle the COW path correctly. After further investigation with the syzbot reproducer and extensive debugging, I found the real issue is in the FITRIM/move_extents code path. The bug occurs when: 1. copy_file_range() creates a reflinked extent with flags=0x2 (OCFS2_EXT_REFCOUNTED) 2. ioctl(FITRIM) is called, which triggers ocfs2_move_extents() 3. In __ocfs2_move_extents_range(), the while loop: - Calls ocfs2_get_clusters() which reads extent with flags=0x2 and caches it - Then calls ocfs2_move_extent() or ocfs2_defrag_extent() - Both eventually call __ocfs2_move_extent() which contains: replace_rec.e_flags = ext_flags & ~OCFS2_EXT_REFCOUNTED; - This clears the refcount flag and writes to disk with flags=0x0 4. However, the extent map cache is NOT cleared after the move operation 5. Cache still contains stale flags=0x2 while disk has flags=0x0 6. Later, when write() triggers COW, ocfs2_refcount_cal_cow_clusters() reads: - From cache: flags=0x2 (stale) - From disk extent tree: flags=0x0 (correct) 7. The mismatch triggers: BUG_ON(!(rec->e_flags & OCFS2_EXT_REFCOUNTED)) The proper fix should be in __ocfs2_move_extents_range() to clear the extent cache after each move/defrag operation completes. I will send a v2 patch with this fix. Thanks, Deepanshu