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sysfs: rename sysfs_assoc_lock and explain what it's about

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sysfs_assoc_lock is an odd piece of locking.  In general, whoever owns
a kobject is responsible for synchronizing sysfs operations and sysfs
proper assumes that, for example, removal won't race with any other
operation; however, this doesn't work for symlinking because an entity
performing symlink doesn't usually own the target kobject and thus has
no control over its removal.

sysfs_assoc_lock synchronizes symlink operations against kobj->sd
disassociation so that symlink code doesn't end up dereferencing
already freed sysfs_dirent by racing with removal of the target
kobject.

This is quite obscure and the generic name of the lock and lack of
comments make it difficult to understand its role.  Let's rename it to
sysfs_symlink_target_lock and add comments explaining what's going on.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tejun Heo
2013-10-30 10:28:36 -04:00
committed by Greg Kroah-Hartman
parent 044e3bc333
commit 0cae60f914
3 changed files with 30 additions and 10 deletions
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2
fs/sysfs/sysfs.h
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@@ -159,7 +159,7 @@ extern struct kmem_cache *sysfs_dir_cachep;
* dir.c
*/
extern struct mutex sysfs_mutex;
extern spinlock_t sysfs_assoc_lock;
extern spinlock_t sysfs_symlink_target_lock;
extern const struct dentry_operations sysfs_dentry_ops;
extern const struct file_operations sysfs_dir_operations;