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authorEric W. Biederman <ebiederm@xmission.com>2010-01-02 16:37:12 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2010-01-04 15:34:46 -0500
commit846f99749ab68bbc7f75c74fec305de675b1a1bf (patch)
tree4c1ca68cfea804bd5215d57844a16f69c566aedc /fs
parent3e27249c84beed1c79d767b350e52ad038db9053 (diff)
sysfs: Add lockdep annotations for the sysfs active reference
Holding locks over device_del -> kobject_del -> sysfs_deactivate can cause deadlocks if those same locks are grabbed in sysfs show or store methods. The I model s_active count + completion as a sleeping read/write lock. I describe to lockdep sysfs_get_active as a read_trylock, sysfs_put_active as a read_unlock, and sysfs_deactivate as a write_lock and write_unlock pair. This seems to capture the essence for purposes of finding deadlocks, and in my testing gives finds real issues and ignores non-issues. This brings us back to holding locks over kobject_del is a problem that ideally we should find a way of addressing, but at least lockdep can tell us about the problems instead of requiring developers to debug rare strange system deadlocks, that happen when sysfs files are removed while being written to. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/sysfs/dir.c14
-rw-r--r--fs/sysfs/sysfs.h15
2 files changed, 27 insertions, 2 deletions
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index f05f2303a8b8..699f371b9f12 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -106,8 +106,10 @@ static struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd)
106 return NULL; 106 return NULL;
107 107
108 t = atomic_cmpxchg(&sd->s_active, v, v + 1); 108 t = atomic_cmpxchg(&sd->s_active, v, v + 1);
109 if (likely(t == v)) 109 if (likely(t == v)) {
110 rwsem_acquire_read(&sd->dep_map, 0, 1, _RET_IP_);
110 return sd; 111 return sd;
112 }
111 if (t < 0) 113 if (t < 0)
112 return NULL; 114 return NULL;
113 115
@@ -130,6 +132,7 @@ static void sysfs_put_active(struct sysfs_dirent *sd)
130 if (unlikely(!sd)) 132 if (unlikely(!sd))
131 return; 133 return;
132 134
135 rwsem_release(&sd->dep_map, 1, _RET_IP_);
133 v = atomic_dec_return(&sd->s_active); 136 v = atomic_dec_return(&sd->s_active);
134 if (likely(v != SD_DEACTIVATED_BIAS)) 137 if (likely(v != SD_DEACTIVATED_BIAS))
135 return; 138 return;
@@ -194,15 +197,21 @@ static void sysfs_deactivate(struct sysfs_dirent *sd)
194 BUG_ON(sd->s_sibling || !(sd->s_flags & SYSFS_FLAG_REMOVED)); 197 BUG_ON(sd->s_sibling || !(sd->s_flags & SYSFS_FLAG_REMOVED));
195 sd->s_sibling = (void *)&wait; 198 sd->s_sibling = (void *)&wait;
196 199
200 rwsem_acquire(&sd->dep_map, 0, 0, _RET_IP_);
197 /* atomic_add_return() is a mb(), put_active() will always see 201 /* atomic_add_return() is a mb(), put_active() will always see
198 * the updated sd->s_sibling. 202 * the updated sd->s_sibling.
199 */ 203 */
200 v = atomic_add_return(SD_DEACTIVATED_BIAS, &sd->s_active); 204 v = atomic_add_return(SD_DEACTIVATED_BIAS, &sd->s_active);
201 205
202 if (v != SD_DEACTIVATED_BIAS) 206 if (v != SD_DEACTIVATED_BIAS) {
207 lock_contended(&sd->dep_map, _RET_IP_);
203 wait_for_completion(&wait); 208 wait_for_completion(&wait);
209 }
204 210
205 sd->s_sibling = NULL; 211 sd->s_sibling = NULL;
212
213 lock_acquired(&sd->dep_map, _RET_IP_);
214 rwsem_release(&sd->dep_map, 1, _RET_IP_);
206} 215}
207 216
208static int sysfs_alloc_ino(ino_t *pino) 217static int sysfs_alloc_ino(ino_t *pino)
@@ -345,6 +354,7 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
345 354
346 atomic_set(&sd->s_count, 1); 355 atomic_set(&sd->s_count, 1);
347 atomic_set(&sd->s_active, 0); 356 atomic_set(&sd->s_active, 0);
357 sysfs_dirent_init_lockdep(sd);
348 358
349 sd->s_name = name; 359 sd->s_name = name;
350 sd->s_mode = mode; 360 sd->s_mode = mode;
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index ca52e7b9d8f8..cdd9377a6e06 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -8,6 +8,7 @@
8 * This file is released under the GPLv2. 8 * This file is released under the GPLv2.
9 */ 9 */
10 10
11#include <linux/lockdep.h>
11#include <linux/fs.h> 12#include <linux/fs.h>
12 13
13struct sysfs_open_dirent; 14struct sysfs_open_dirent;
@@ -50,6 +51,9 @@ struct sysfs_inode_attrs {
50struct sysfs_dirent { 51struct sysfs_dirent {
51 atomic_t s_count; 52 atomic_t s_count;
52 atomic_t s_active; 53 atomic_t s_active;
54#ifdef CONFIG_DEBUG_LOCK_ALLOC
55 struct lockdep_map dep_map;
56#endif
53 struct sysfs_dirent *s_parent; 57 struct sysfs_dirent *s_parent;
54 struct sysfs_dirent *s_sibling; 58 struct sysfs_dirent *s_sibling;
55 const char *s_name; 59 const char *s_name;
@@ -84,6 +88,17 @@ static inline unsigned int sysfs_type(struct sysfs_dirent *sd)
84 return sd->s_flags & SYSFS_TYPE_MASK; 88 return sd->s_flags & SYSFS_TYPE_MASK;
85} 89}
86 90
91#ifdef CONFIG_DEBUG_LOCK_ALLOC
92#define sysfs_dirent_init_lockdep(sd) \
93do { \
94 static struct lock_class_key __key; \
95 \
96 lockdep_init_map(&sd->dep_map, "s_active", &__key, 0); \
97} while(0)
98#else
99#define sysfs_dirent_init_lockdep(sd) do {} while(0)
100#endif
101
87/* 102/*
88 * Context structure to be used while adding/removing nodes. 103 * Context structure to be used while adding/removing nodes.
89 */ 104 */