From 846f99749ab68bbc7f75c74fec305de675b1a1bf Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Sat, 2 Jan 2010 13:37:12 -0800 Subject: [PATCH] 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 Acked-by: Tejun Heo Signed-off-by: Linus Torvalds --- fs/sysfs/dir.c | 14 ++++++++++++-- fs/sysfs/sysfs.h | 15 +++++++++++++++ 2 files changed, 27 insertions(+), 2 deletions(-) diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c index f05f230..699f371 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) return NULL; t = atomic_cmpxchg(&sd->s_active, v, v + 1); - if (likely(t == v)) + if (likely(t == v)) { + rwsem_acquire_read(&sd->dep_map, 0, 1, _RET_IP_); return sd; + } if (t < 0) return NULL; @@ -130,6 +132,7 @@ static void sysfs_put_active(struct sysfs_dirent *sd) if (unlikely(!sd)) return; + rwsem_release(&sd->dep_map, 1, _RET_IP_); v = atomic_dec_return(&sd->s_active); if (likely(v != SD_DEACTIVATED_BIAS)) return; @@ -194,15 +197,21 @@ static void sysfs_deactivate(struct sysfs_dirent *sd) BUG_ON(sd->s_sibling || !(sd->s_flags & SYSFS_FLAG_REMOVED)); sd->s_sibling = (void *)&wait; + rwsem_acquire(&sd->dep_map, 0, 0, _RET_IP_); /* atomic_add_return() is a mb(), put_active() will always see * the updated sd->s_sibling. */ v = atomic_add_return(SD_DEACTIVATED_BIAS, &sd->s_active); - if (v != SD_DEACTIVATED_BIAS) + if (v != SD_DEACTIVATED_BIAS) { + lock_contended(&sd->dep_map, _RET_IP_); wait_for_completion(&wait); + } sd->s_sibling = NULL; + + lock_acquired(&sd->dep_map, _RET_IP_); + rwsem_release(&sd->dep_map, 1, _RET_IP_); } static 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) atomic_set(&sd->s_count, 1); atomic_set(&sd->s_active, 0); + sysfs_dirent_init_lockdep(sd); sd->s_name = name; sd->s_mode = mode; diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h index ca52e7b..cdd9377 100644 --- a/fs/sysfs/sysfs.h +++ b/fs/sysfs/sysfs.h @@ -8,6 +8,7 @@ * This file is released under the GPLv2. */ +#include #include struct sysfs_open_dirent; @@ -50,6 +51,9 @@ struct sysfs_inode_attrs { struct sysfs_dirent { atomic_t s_count; atomic_t s_active; +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lockdep_map dep_map; +#endif struct sysfs_dirent *s_parent; struct sysfs_dirent *s_sibling; const char *s_name; @@ -84,6 +88,17 @@ static inline unsigned int sysfs_type(struct sysfs_dirent *sd) return sd->s_flags & SYSFS_TYPE_MASK; } +#ifdef CONFIG_DEBUG_LOCK_ALLOC +#define sysfs_dirent_init_lockdep(sd) \ +do { \ + static struct lock_class_key __key; \ + \ + lockdep_init_map(&sd->dep_map, "s_active", &__key, 0); \ +} while(0) +#else +#define sysfs_dirent_init_lockdep(sd) do {} while(0) +#endif + /* * Context structure to be used while adding/removing nodes. */ -- 1.8.2.3