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kernfs: fix potential NULL dereference in __kernfs_remove 

When lockdep is enabled, lockdep_assert_held_write would
cause potential NULL pointer dereference.

Fix the following smatch warnings:

fs/kernfs/dir.c:1353 __kernfs_remove() warn: variable dereferenced before check 'kn' (see line 1346)

Fixes: 393c371408 ("kernfs: switch global kernfs_rwsem lock to per-fs lock")
Signed-off-by: Yushan Zhou <katrinzhou@tencent.com>
Link: https://lore.kernel.org/r/20220630082512.3482581-1-zys.zljxml@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Yushan Zhou 2022-06-30 16:25:12 +08:00 committed by Greg Kroah-Hartman
parent c882716b6d
commit 72b5d5aef2
1 changed files with 5 additions and 2 deletions
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7
fs/kernfs/dir.c
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@ -1343,14 +1343,17 @@ static void __kernfs_remove(struct kernfs_node *kn)
{ {
struct kernfs_node *pos; struct kernfs_node *pos;
/* Short-circuit if non-root @kn has already finished removal. */
if (!kn)
return;
lockdep_assert_held_write(&kernfs_root(kn)->kernfs_rwsem); lockdep_assert_held_write(&kernfs_root(kn)->kernfs_rwsem);
/* /*
* Short-circuit if non-root @kn has already finished removal.
* This is for kernfs_remove_self() which plays with active ref * This is for kernfs_remove_self() which plays with active ref
* after removal. * after removal.
*/ */
if (!kn || (kn->parent && RB_EMPTY_NODE(&kn->rb))) if (kn->parent && RB_EMPTY_NODE(&kn->rb))
return; return;
pr_debug("kernfs %s: removing\n", kn->name); pr_debug("kernfs %s: removing\n", kn->name);