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authorTejun Heo <tj@kernel.org>2013-10-30 10:28:36 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-11-01 12:13:37 -0700
commit0cae60f91494e34a0c5391f1455f825d5849b05f (patch)
tree56746a582c79df11a88fe0016ea4919c018d5553 /fs/sysfs/symlink.c
parent044e3bc33391b1f2769d5ab2c04f246c3d8e04c3 (diff)
downloadop-kernel-dev-0cae60f91494e34a0c5391f1455f825d5849b05f.zip
op-kernel-dev-0cae60f91494e34a0c5391f1455f825d5849b05f.tar.gz
sysfs: rename sysfs_assoc_lock and explain what it's about
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>
Diffstat (limited to 'fs/sysfs/symlink.c')
-rw-r--r--fs/sysfs/symlink.c20
1 files changed, 14 insertions, 6 deletions
diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
index 22ea2f5..1a23681 100644
--- a/fs/sysfs/symlink.c
+++ b/fs/sysfs/symlink.c
@@ -32,13 +32,15 @@ static int sysfs_do_create_link_sd(struct sysfs_dirent *parent_sd,
BUG_ON(!name || !parent_sd);
- /* target->sd can go away beneath us but is protected with
- * sysfs_assoc_lock. Fetch target_sd from it.
+ /*
+ * We don't own @target and it may be removed at any time.
+ * Synchronize using sysfs_symlink_target_lock. See
+ * sysfs_remove_dir() for details.
*/
- spin_lock(&sysfs_assoc_lock);
+ spin_lock(&sysfs_symlink_target_lock);
if (target->sd)
target_sd = sysfs_get(target->sd);
- spin_unlock(&sysfs_assoc_lock);
+ spin_unlock(&sysfs_symlink_target_lock);
error = -ENOENT;
if (!target_sd)
@@ -140,10 +142,16 @@ void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
const char *name)
{
const void *ns = NULL;
- spin_lock(&sysfs_assoc_lock);
+
+ /*
+ * We don't own @target and it may be removed at any time.
+ * Synchronize using sysfs_symlink_target_lock. See
+ * sysfs_remove_dir() for details.
+ */
+ spin_lock(&sysfs_symlink_target_lock);
if (targ->sd)
ns = targ->sd->s_ns;
- spin_unlock(&sysfs_assoc_lock);
+ spin_unlock(&sysfs_symlink_target_lock);
sysfs_hash_and_remove(kobj->sd, name, ns);
}
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