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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 badc28d492 ("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 f95bdb700b ("mm: vmscan: make global slab
shrink lockless") made the race condition more likely, though it existed
before then.
Commit badc28d492 ("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 20cd1892fc
("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: badc28d492 ("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>
137 lines
4.4 KiB
C
137 lines
4.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_SHRINKER_H
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#define _LINUX_SHRINKER_H
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#include <linux/atomic.h>
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#include <linux/types.h>
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/*
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* This struct is used to pass information from page reclaim to the shrinkers.
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* We consolidate the values for easier extension later.
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*
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* The 'gfpmask' refers to the allocation we are currently trying to
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* fulfil.
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*/
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struct shrink_control {
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gfp_t gfp_mask;
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/* current node being shrunk (for NUMA aware shrinkers) */
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int nid;
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/*
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* How many objects scan_objects should scan and try to reclaim.
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* This is reset before every call, so it is safe for callees
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* to modify.
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*/
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unsigned long nr_to_scan;
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/*
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* How many objects did scan_objects process?
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* This defaults to nr_to_scan before every call, but the callee
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* should track its actual progress.
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*/
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unsigned long nr_scanned;
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/* current memcg being shrunk (for memcg aware shrinkers) */
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struct mem_cgroup *memcg;
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};
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#define SHRINK_STOP (~0UL)
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#define SHRINK_EMPTY (~0UL - 1)
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/*
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* A callback you can register to apply pressure to ageable caches.
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*
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* @count_objects should return the number of freeable items in the cache. If
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* there are no objects to free, it should return SHRINK_EMPTY, while 0 is
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* returned in cases of the number of freeable items cannot be determined
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* or shrinker should skip this cache for this time (e.g., their number
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* is below shrinkable limit). No deadlock checks should be done during the
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* count callback - the shrinker relies on aggregating scan counts that couldn't
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* be executed due to potential deadlocks to be run at a later call when the
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* deadlock condition is no longer pending.
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*
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* @scan_objects will only be called if @count_objects returned a non-zero
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* value for the number of freeable objects. The callout should scan the cache
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* and attempt to free items from the cache. It should then return the number
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* of objects freed during the scan, or SHRINK_STOP if progress cannot be made
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* due to potential deadlocks. If SHRINK_STOP is returned, then no further
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* attempts to call the @scan_objects will be made from the current reclaim
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* context.
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*
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* @flags determine the shrinker abilities, like numa awareness
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*/
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struct shrinker {
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unsigned long (*count_objects)(struct shrinker *,
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struct shrink_control *sc);
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unsigned long (*scan_objects)(struct shrinker *,
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struct shrink_control *sc);
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long batch; /* reclaim batch size, 0 = default */
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int seeks; /* seeks to recreate an obj */
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unsigned flags;
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/* These are for internal use */
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struct list_head list;
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#ifdef CONFIG_MEMCG
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/* ID in shrinker_idr */
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int id;
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#endif
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#ifdef CONFIG_SHRINKER_DEBUG
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int debugfs_id;
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const char *name;
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struct dentry *debugfs_entry;
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#endif
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/* objs pending delete, per node */
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atomic_long_t *nr_deferred;
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};
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#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
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/* Flags */
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#define SHRINKER_REGISTERED (1 << 0)
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#define SHRINKER_NUMA_AWARE (1 << 1)
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#define SHRINKER_MEMCG_AWARE (1 << 2)
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/*
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* It just makes sense when the shrinker is also MEMCG_AWARE for now,
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* non-MEMCG_AWARE shrinker should not have this flag set.
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*/
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#define SHRINKER_NONSLAB (1 << 3)
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extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker,
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const char *fmt, ...);
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extern void register_shrinker_prepared(struct shrinker *shrinker);
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extern int __printf(2, 3) register_shrinker(struct shrinker *shrinker,
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const char *fmt, ...);
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extern void unregister_shrinker(struct shrinker *shrinker);
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extern void free_prealloced_shrinker(struct shrinker *shrinker);
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extern void synchronize_shrinkers(void);
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#ifdef CONFIG_SHRINKER_DEBUG
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extern int shrinker_debugfs_add(struct shrinker *shrinker);
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extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
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int *debugfs_id);
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extern void shrinker_debugfs_remove(struct dentry *debugfs_entry,
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int debugfs_id);
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extern int __printf(2, 3) shrinker_debugfs_rename(struct shrinker *shrinker,
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const char *fmt, ...);
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#else /* CONFIG_SHRINKER_DEBUG */
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static inline int shrinker_debugfs_add(struct shrinker *shrinker)
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{
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return 0;
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}
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static inline struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
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int *debugfs_id)
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{
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*debugfs_id = -1;
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return NULL;
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}
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static inline void shrinker_debugfs_remove(struct dentry *debugfs_entry,
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int debugfs_id)
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{
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}
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static inline __printf(2, 3)
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int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
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{
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return 0;
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}
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#endif /* CONFIG_SHRINKER_DEBUG */
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#endif /* _LINUX_SHRINKER_H */
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