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authorJoan Bruguera Micó <joanbrugueram@gmail.com>2023-05-03 04:32:32 +0300
committerAndrew Morton <akpm@linux-foundation.org>2023-05-18 01:24:33 +0300
commit26e239b37ebdfd189a2e6f94d3407e70313348bc (patch)
tree3500b95b4929aef1da588cb5b0ddb2886b8b4a7c /include
parent0257d9908d38c0b1669af4bb1bc4dbca1f273fe6 (diff)
downloadlinux-26e239b37ebdfd189a2e6f94d3407e70313348bc.tar.xz
mm: shrinkers: fix race condition on debugfs cleanup
When something registers and unregisters many shrinkers, such as: for x in $(seq 10000); do unshare -Ui true; done Sometimes the following error is printed to the kernel log: debugfs: Directory '...' with parent 'shrinker' already present! This occurs since commit badc28d4924b ("mm: shrinkers: fix deadlock in shrinker debugfs") / v6.2: Since the call to `debugfs_remove_recursive` was moved outside the `shrinker_rwsem`/`shrinker_mutex` lock, but the call to `ida_free` stayed inside, a newly registered shrinker can be re-assigned that ID and attempt to create the debugfs directory before the directory from the previous shrinker has been removed. The locking changes in commit f95bdb700bc6 ("mm: vmscan: make global slab shrink lockless") made the race condition more likely, though it existed before then. Commit badc28d4924b ("mm: shrinkers: fix deadlock in shrinker debugfs") could be reverted since the issue is addressed should no longer occur since the count and scan operations are lockless since commit 20cd1892fcc3 ("mm: shrinkers: make count and scan in shrinker debugfs lockless"). However, since this is a contended lock, prefer instead moving `ida_free` outside the lock to avoid the race. Link: https://lkml.kernel.org/r/20230503013232.299211-1-joanbrugueram@gmail.com Fixes: badc28d4924b ("mm: shrinkers: fix deadlock in shrinker debugfs") Signed-off-by: Joan Bruguera Micó <joanbrugueram@gmail.com> Cc: Qi Zheng <zhengqi.arch@bytedance.com> Cc: Roman Gushchin <roman.gushchin@linux.dev> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/shrinker.h13
1 files changed, 11 insertions, 2 deletions
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 7bde8e1c228a..224293b2dd06 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -107,7 +107,10 @@ extern void synchronize_shrinkers(void);
#ifdef CONFIG_SHRINKER_DEBUG
extern int shrinker_debugfs_add(struct shrinker *shrinker);
-extern struct dentry *shrinker_debugfs_remove(struct shrinker *shrinker);
+extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
+ int *debugfs_id);
+extern void shrinker_debugfs_remove(struct dentry *debugfs_entry,
+ int debugfs_id);
extern int __printf(2, 3) shrinker_debugfs_rename(struct shrinker *shrinker,
const char *fmt, ...);
#else /* CONFIG_SHRINKER_DEBUG */
@@ -115,10 +118,16 @@ static inline int shrinker_debugfs_add(struct shrinker *shrinker)
{
return 0;
}
-static inline struct dentry *shrinker_debugfs_remove(struct shrinker *shrinker)
+static inline struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
+ int *debugfs_id)
{
+ *debugfs_id = -1;
return NULL;
}
+static inline void shrinker_debugfs_remove(struct dentry *debugfs_entry,
+ int debugfs_id)
+{
+}
static inline __printf(2, 3)
int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
{