Messages in this thread | | | From | Nguyen Dinh Phi <> | Subject | Re: [PATCH] kernfs: switch global kernfs_rwsem lock to per-fs lock | Date | Mon, 29 Nov 2021 22:23:16 +0800 |
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>This patch landed recently in linux-next (20211126) as commit >393c3714081a ("kernfs: switch global kernfs_rwsem lock to per-fs lock"). >In my tests I've found that it causes the following warning during the >system reboot: > > ========================= > WARNING: held lock freed! > 5.16.0-rc2+ #10984 Not tainted > ------------------------- > kworker/1:0/18 is freeing memory ffff00004034e200-ffff00004034e3ff, >with a lock still held there! > ffff00004034e348 (&root->kernfs_rwsem){++++}-{3:3}, at: >__kernfs_remove+0x310/0x37c > 3 locks held by kworker/1:0/18: > #0: ffff000040107938 ((wq_completion)cgroup_destroy){+.+.}-{0:0}, at: >process_one_work+0x1f0/0x6f0 > #1: ffff80000b55bdc0 >((work_completion)(&(&css->destroy_rwork)->work)){+.+.}-{0:0}, at: >process_one_work+0x1f0/0x6f0 > #2: ffff00004034e348 (&root->kernfs_rwsem){++++}-{3:3}, at: >__kernfs_remove+0x310/0x37c > > stack backtrace: > CPU: 1 PID: 18 Comm: kworker/1:0 Not tainted 5.16.0-rc2+ #10984 > Hardware name: Raspberry Pi 4 Model B (DT) > Workqueue: cgroup_destroy css_free_rwork_fn > Call trace: > dump_backtrace+0x0/0x1ac > show_stack+0x18/0x24 > dump_stack_lvl+0x8c/0xb8 > dump_stack+0x18/0x34 > debug_check_no_locks_freed+0x124/0x140 > kfree+0xf0/0x3a4 > kernfs_put+0x1f8/0x224 > __kernfs_remove+0x1b8/0x37c > kernfs_destroy_root+0x38/0x50 > css_free_rwork_fn+0x288/0x3d4 > process_one_work+0x288/0x6f0 > worker_thread+0x74/0x470 > kthread+0x188/0x194 > ret_from_fork+0x10/0x20 > >Let me know if you need more information or help in reproducing this issue.
This patch has a problem, in function kernfs_remove(), it call to __kernfs_remove(kn), which will free the related @root of @kn, it means the root->kernfs_rwsem will be freed too, but it is still being held by the call to down_write(&root->kernfs_rwsem) around line number 100.
BR
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