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linux-yocto/fs/kernfs
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Michal Koutný 6c81f1c781 kernfs: Relax constraint in draining guard 
[ Upstream commit 071d8e4c2a ]

The active reference lifecycle provides the break/unbreak mechanism but
the active reference is not truly active after unbreak -- callers don't
use it afterwards but it's important for proper pairing of kn->active
counting. Assuming this mechanism is in place, the WARN check in
kernfs_should_drain_open_files() is too sensitive -- it may transiently
catch those (rightful) callers between
kernfs_unbreak_active_protection() and kernfs_put_active() as found out by Chen
Ridong:

	kernfs_remove_by_name_ns	kernfs_get_active // active=1
	__kernfs_remove					  // active=0x80000002
	kernfs_drain			...
	wait_event
	//waiting (active == 0x80000001)
					kernfs_break_active_protection
					// active = 0x80000001
	// continue
					kernfs_unbreak_active_protection
					// active = 0x80000002
	...
	kernfs_should_drain_open_files
	// warning occurs
					kernfs_put_active

To avoid the false positives (mind panic_on_warn) remove the check altogether.
(This is meant as quick fix, I think active reference break/unbreak may be
simplified with larger rework.)

Fixes: bdb2fd7fc5 ("kernfs: Skip kernfs_drain_open_files() more aggressively")
Link: https://lore.kernel.org/r/kmmrseckjctb4gxcx2rdminrjnq2b4ipf7562nvfd432ld5v5m@2byj5eedkb2o/

Cc: Chen Ridong <chenridong@huawei.com>
Signed-off-by: Michal Koutný <mkoutny@suse.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20250505121201.879823-1-mkoutny@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2025-06-19 15:28:16 +02:00
..
dir.c kernfs: Relax constraint in draining guard 2025-06-19 15:28:16 +02:00
file.c kernfs: Relax constraint in draining guard 2025-06-19 15:28:16 +02:00
inode.c v6.6-vfs.tmpfs 2023-08-28 09:55:25 -07:00
Kconfig
kernfs-internal.h kernfs: RCU protect kernfs_nodes and avoid kernfs_idr_lock in kernfs_find_and_get_node_by_id() 2024-04-13 13:07:38 +02:00
Makefile
mount.c kernfs: attach uuid for every kernfs and report it in fsid 2023-08-05 08:32:39 +02:00
symlink.c kernfs: fix all kernel-doc warnings and multiple typos 2022-11-23 19:28:26 +01:00