mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
synced 2025-01-18 06:15:12 +00:00
26e239b37e
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>
138 lines
4.4 KiB
C
138 lines
4.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
#ifndef _LINUX_SHRINKER_H
|
|
#define _LINUX_SHRINKER_H
|
|
|
|
#include <linux/atomic.h>
|
|
#include <linux/types.h>
|
|
|
|
/*
|
|
* This struct is used to pass information from page reclaim to the shrinkers.
|
|
* We consolidate the values for easier extension later.
|
|
*
|
|
* The 'gfpmask' refers to the allocation we are currently trying to
|
|
* fulfil.
|
|
*/
|
|
struct shrink_control {
|
|
gfp_t gfp_mask;
|
|
|
|
/* current node being shrunk (for NUMA aware shrinkers) */
|
|
int nid;
|
|
|
|
/*
|
|
* How many objects scan_objects should scan and try to reclaim.
|
|
* This is reset before every call, so it is safe for callees
|
|
* to modify.
|
|
*/
|
|
unsigned long nr_to_scan;
|
|
|
|
/*
|
|
* How many objects did scan_objects process?
|
|
* This defaults to nr_to_scan before every call, but the callee
|
|
* should track its actual progress.
|
|
*/
|
|
unsigned long nr_scanned;
|
|
|
|
/* current memcg being shrunk (for memcg aware shrinkers) */
|
|
struct mem_cgroup *memcg;
|
|
};
|
|
|
|
#define SHRINK_STOP (~0UL)
|
|
#define SHRINK_EMPTY (~0UL - 1)
|
|
/*
|
|
* A callback you can register to apply pressure to ageable caches.
|
|
*
|
|
* @count_objects should return the number of freeable items in the cache. If
|
|
* there are no objects to free, it should return SHRINK_EMPTY, while 0 is
|
|
* returned in cases of the number of freeable items cannot be determined
|
|
* or shrinker should skip this cache for this time (e.g., their number
|
|
* is below shrinkable limit). No deadlock checks should be done during the
|
|
* count callback - the shrinker relies on aggregating scan counts that couldn't
|
|
* be executed due to potential deadlocks to be run at a later call when the
|
|
* deadlock condition is no longer pending.
|
|
*
|
|
* @scan_objects will only be called if @count_objects returned a non-zero
|
|
* value for the number of freeable objects. The callout should scan the cache
|
|
* and attempt to free items from the cache. It should then return the number
|
|
* of objects freed during the scan, or SHRINK_STOP if progress cannot be made
|
|
* due to potential deadlocks. If SHRINK_STOP is returned, then no further
|
|
* attempts to call the @scan_objects will be made from the current reclaim
|
|
* context.
|
|
*
|
|
* @flags determine the shrinker abilities, like numa awareness
|
|
*/
|
|
struct shrinker {
|
|
unsigned long (*count_objects)(struct shrinker *,
|
|
struct shrink_control *sc);
|
|
unsigned long (*scan_objects)(struct shrinker *,
|
|
struct shrink_control *sc);
|
|
|
|
long batch; /* reclaim batch size, 0 = default */
|
|
int seeks; /* seeks to recreate an obj */
|
|
unsigned flags;
|
|
|
|
/* These are for internal use */
|
|
struct list_head list;
|
|
#ifdef CONFIG_MEMCG
|
|
/* ID in shrinker_idr */
|
|
int id;
|
|
#endif
|
|
#ifdef CONFIG_SHRINKER_DEBUG
|
|
int debugfs_id;
|
|
const char *name;
|
|
struct dentry *debugfs_entry;
|
|
#endif
|
|
/* objs pending delete, per node */
|
|
atomic_long_t *nr_deferred;
|
|
};
|
|
#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
|
|
|
|
/* Flags */
|
|
#define SHRINKER_REGISTERED (1 << 0)
|
|
#define SHRINKER_NUMA_AWARE (1 << 1)
|
|
#define SHRINKER_MEMCG_AWARE (1 << 2)
|
|
/*
|
|
* It just makes sense when the shrinker is also MEMCG_AWARE for now,
|
|
* non-MEMCG_AWARE shrinker should not have this flag set.
|
|
*/
|
|
#define SHRINKER_NONSLAB (1 << 3)
|
|
|
|
extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker,
|
|
const char *fmt, ...);
|
|
extern void register_shrinker_prepared(struct shrinker *shrinker);
|
|
extern int __printf(2, 3) register_shrinker(struct shrinker *shrinker,
|
|
const char *fmt, ...);
|
|
extern void unregister_shrinker(struct shrinker *shrinker);
|
|
extern void free_prealloced_shrinker(struct shrinker *shrinker);
|
|
extern void synchronize_shrinkers(void);
|
|
|
|
#ifdef CONFIG_SHRINKER_DEBUG
|
|
extern int shrinker_debugfs_add(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 */
|
|
static inline int shrinker_debugfs_add(struct shrinker *shrinker)
|
|
{
|
|
return 0;
|
|
}
|
|
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, ...)
|
|
{
|
|
return 0;
|
|
}
|
|
#endif /* CONFIG_SHRINKER_DEBUG */
|
|
#endif /* _LINUX_SHRINKER_H */
|