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Thu, 27 Aug 2026 21:03:27 -0700 (PDT) Received: from google.com ([2a00:79e0:2031:6:ff0:ad84:24b0:9e52]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-396db196903sm790271a91.0.2026.08.27.21.03.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Aug 2026 21:03:26 -0700 (PDT) Date: Fri, 28 Aug 2026 13:03:23 +0900 From: Sergey Senozhatsky To: Jan Kara Cc: Sergey Senozhatsky , Theodore Ts'o , Andreas Dilger , Baokun Li , Ojaswin Mujoo , "Ritesh Harjani (IBM)" , Zhang Yi , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, Sarthak Kukreti Subject: Re: [PATCH] fs/ext4: fix ABBA deadlock in ext4_rmdir() Message-ID: References: <20260827125158.4030598-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-ext4@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: On (26/08/27 15:41), Jan Kara wrote: > On Thu 27-08-26 21:50:20, Sergey Senozhatsky wrote: > > We observe the following ABBA deadlock (casefolding enabled): > > > > INFO: task jbd2/dm-13-8:447 blocked for more than 720 seconds. > > task:jbd2/dm-13-8 state:D stack:0 pid:447 tgid:447 ppid:2 > > Call Trace: > > > > __schedule+0xc2c/0xe60 > > schedule+0x40/0xe0 > > jbd2_journal_wait_updates+0x8f/0xf0 > > jbd2_journal_commit_transaction+0x321/0x1850 > > kjournald2+0xa9/0x230 > > kthread+0x226/0x2a0 > > ret_from_fork+0x101/0x1e0 > > ret_from_fork_asm+0x1a/0x30 > > > > INFO: task Thread-10:4161 blocked for more than 720 seconds. > > task:Thread-10 state:D stack:0 pid:4161 tgid:3848 ppid:540 > > Call Trace: > > > > __schedule+0xc2c/0xe60 > > schedule+0x40/0xe0 > > wait_transaction_locked+0x8c/0xd0 > > start_this_handle+0x252/0x870 > > jbd2__journal_start+0x120/0x280 > > __ext4_journal_start_sb+0x11a/0x250 > > ext4_evict_inode+0x208/0x760 > > iput+0x222/0x5c0 > > dput+0x293/0x690 > > ____fput+0x145/0x2b0 > > task_work_run+0x7a/0xb0 > > exit_to_user_mode_loop+0xc0/0xd0 > > do_syscall_64+0x14b/0xf10 > > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > > > NMI backtrace for cpu 0 > > CPU: 0 UID: 1010216 PID: 4160 Comm: Thread-7 > > RIP: 0010:d_walk+0x0/0x290 > > [..] > > Call Trace: > > > > shrink_dcache_parent+0xb2/0x100 > > d_invalidate+0x50/0x110 > > ext4_rmdir+0x3a2/0x3d0 > > vfs_rmdir+0x9d/0x1d0 > > do_rmdir+0xf0/0x330 > > __x64_sys_unlinkat+0x34/0x50 > > do_syscall_64+0x61/0xf10 > > > > The problem is that ext4_rmdir() calls d_invalidate() before stopping > > the jbd2 transaction handle. Because d_invalidate() traverses child > > dentries it can encounter dying or in-use dentries. If a concurrent > > thread executing __dentry_kill() on a child dentry invokes ext4_evict_inode(), > > it requests a new transaction handle via ext4_journal_start(), which > > waits for all running handles to close. However, the thread executing > > ext4_rmdir() still holds its active transaction handle while looping > > in shrink_dcache_parent() waiting for the dying child dentry to complete > > eviction. > > > > Stop transaction handle in ext4_rmdir() before calling d_invalidate(). > > > > Fixes: b886ee3e778e ("ext4: Support case-insensitive file name lookups") > > Co-developed-by: Sarthak Kukreti > > Signed-off-by: Sarthak Kukreti > > Signed-off-by: Sergey Senozhatsky > > Good catch! Feel free to add: > > Reviewed-by: Jan Kara Thanks!