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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-78e6a40fc41sm864367b3.29.2025.12.11.19.56.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Dec 2025 19:56:49 -0800 (PST) Date: Thu, 11 Dec 2025 19:56:38 -0800 (PST) From: Hugh Dickins To: Al Viro cc: Christian Brauner , Andrew Morton , Baolin Wang , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: 6.19 tmpfs __d_lookup() lockup Message-ID: <47e9d03c-7a50-2c7d-247d-36f95a5329ed@google.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 Hi Al, Though good for ordinary usage, your persistency mods for 6.19 cause tmpfs to lockup in __d_lookup() during several fsstressing xfstests: fairly reliably in generic/269, generic/476, generic/650, generic/750, less reliably in generic/013, generic/585. Typical dmesg below. I have not spotted what's wrong: better hand over to you. Of course, 2313598222f9 ("convert ramfs and tmpfs") (of Feb 26 2024!) comes out as the first failing commit, no surprise there. I did try inserting a BUG_ON(node == node->next) on line 2438 of fs/dcache.c, just after __d_lookup's hlist_bl_for_each_entry_rcu(), and that BUG was immediately hit (but, for all I know, perhaps that's an unreliable asserition, perhaps it's acceptable for a race to result in a momentary node == node->next there). I did try hacking on xfstests common/rc, to allow ramfs where tmpfs is enabled (and _df_device() then needs $DF_PROG -a to show ramfs). I did not get a lockup or crash from any of them on ramfs (and 476 and 750 actually passed). I don't draw any conclusion from that, maybe ramfs just does not support some of the options which help fsstress to generate the issue; but it might be useful background info. Hoping you can soon guess what's gone wrong, or ask for more info, thanks, Hugh [ 54.354788] run fstests generic/269 at 2025-12-10 19:40:16 [ 114.660512] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: [ 114.670705] rcu: Tasks blocked on level-0 rcu_node (CPUs 0-7): P3185 [ 114.681006] rcu: (detected by 6, t=15007 jiffies, g=3377, q=6940 ncpus=8) [ 114.691346] task:fsstress state:R running task stack:0 pid:3185 tgid:3185 ppid:3059 task_flags:0x400140 flags:0x00080003 [ 114.702226] Call Trace: [ 114.712908] [ 114.723528] __schedule+0x67c/0x6c5 [ 114.734245] ? __d_lookup_rcu+0x7a/0x9c [ 114.744921] ? irqentry_exit+0x27/0x35 [ 114.755547] ? sysvec_apic_timer_interrupt+0xa8/0xae [ 114.766300] ? asm_sysvec_apic_timer_interrupt+0x1b/0x20 [ 114.776953] ? __d_lookup+0x37/0xad [ 114.787357] ? __d_lookup+0x2f/0xad [ 114.797700] ? d_lookup+0x2b/0x42 [ 114.807970] ? lookup_dcache+0x1f/0x60 [ 114.818265] ? lookup_one_qstr_excl+0x1a/0xbe [ 114.828525] ? do_renameat2+0x1d1/0x3e4 [ 114.838808] ? getname_flags+0x4b/0x17a [ 114.849093] ? __do_sys_rename+0x36/0x3e [ 114.859363] ? __x64_sys_rename+0x11/0x13 [ 114.869634] ? x64_sys_call+0x34d/0xe2c [ 114.879797] ? do_syscall_64+0x53/0x123 [ 114.889820] ? entry_SYSCALL_64_after_hwframe+0x4b/0x53 [ 114.899748]