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Subject[PATCH RFC 1/1] kernfs: keep kernfs node alive for __kernfs_remove()
Date
__kernfs_remove() which is called under kernfs_mutex,
assumes nobody kills kernfs node whie it's working on it
and "get"s current kernfs node for that.

But we hit a warning in kernfs_get(): kn->counter == 0 already:
------------[ cut here ]------------
WARNING: CPU: 2 PID: 63923 at fs/kernfs/dir.c:377 kernfs_get+0x2f/0x40
...
Call Trace:
[<ffffffffa7f92e67>] dump_stack+0x19/0x1b
[<ffffffffa78987b8>] __warn+0xd8/0x100
[<ffffffffa78988fd>] warn_slowpath_null+0x1d/0x20
[<ffffffffa7aecaff>] kernfs_get+0x2f/0x40
[<ffffffffa7aed233>] __kernfs_remove+0x113/0x260
[<ffffffffa7aee201>] kernfs_remove+0x21/0x30
[<ffffffffa7af1010>] sysfs_remove_dir+0x50/0x80
[<ffffffffa7b9fb38>] kobject_del+0x18/0x50
[<ffffffffa7a38a4d>] sysfs_slab_remove+0x3d/0x50
[<ffffffffa79f1e6b>] do_kmem_cache_release+0x3b/0x70
[<ffffffffa79f2aa1>] memcg_destroy_kmem_caches+0xb1/0xf0
[<ffffffffa7a4ed5c>] mem_cgroup_css_free+0x4c/0x280
[<ffffffffa79377fc>] cgroup_free_fn+0x4c/0x120
[<ffffffffa78bc222>] process_one_work+0x182/0x440
[<ffffffffa78bd3d6>] worker_thread+0x126/0x3c0
[<ffffffffa78c4441>] kthread+0xd1/0xe0

This could be for example because of kernfs_notify_workfn() which
does kernfs_put(kn) out of kernfs_mutex held section,
so move kernfs_put(kn) under the mutex.

Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
---
fs/kernfs/file.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index ae948aaa4c53..ab9c7e2064cc 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -915,8 +915,8 @@ static void kernfs_notify_workfn(struct work_struct *work)
iput(inode);
}

- mutex_unlock(&kernfs_mutex);
kernfs_put(kn);
+ mutex_unlock(&kernfs_mutex);
goto repeat;
}

--
2.15.1
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