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badc28d492
The debugfs_remove_recursive() is invoked by unregister_shrinker(), which
is holding the write lock of shrinker_rwsem. It will waits for the
handler of debugfs file complete. The handler also needs to hold the read
lock of shrinker_rwsem to do something. So it may cause the following
deadlock:
CPU0 CPU1
debugfs_file_get()
shrinker_debugfs_count_show()/shrinker_debugfs_scan_write()
unregister_shrinker()
--> down_write(&shrinker_rwsem);
debugfs_remove_recursive()
// wait for (A)
--> wait_for_completion();
// wait for (B)
--> down_read_killable(&shrinker_rwsem)
debugfs_file_put() -- (A)
up_write() -- (B)
The down_read_killable() can be killed, so that the above deadlock can be
recovered. But it still requires an extra kill action, otherwise it will
block all subsequent shrinker-related operations, so it's better to fix
it.
[akpm@linux-foundation.org: fix CONFIG_SHRINKER_DEBUG=n stub]
Link: https://lkml.kernel.org/r/20230202105612.64641-1-zhengqi.arch@bytedance.com
Fixes: 5035ebc644 ("mm: shrinkers: introduce debugfs interface for memory shrinkers")
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
128 lines
4.2 KiB
C
128 lines
4.2 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_remove(struct shrinker *shrinker);
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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_remove(struct shrinker *shrinker)
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{
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return NULL;
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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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