[PATCH 1/3] jbd2,rcu: correctly use RCU
From: Lai Jiangshan <hidden>
Date: 2011-06-16 01:47:53
Also in:
lkml
Subsystem:
filesystems (vfs and infrastructure), journalling layer for block devices (jbd2), the rest · Maintainers:
Alexander Viro, Christian Brauner, "Theodore Ts'o", Jan Kara, Linus Torvalds
In read site, we need to use local_ptr = rcu_dereference(), and then use this local_ptr to read the content. In update site, we should assign/publish the new object/pointer after the content of the new object/pointer is fully initialized, and we can't not touch the object after the pointer assignment. rcu_assign_pointer() is need for the assignement. Signed-off-by: Lai Jiangshan <redacted> --- fs/jbd2/journal.c | 25 +++++++++++++------------ 1 files changed, 13 insertions(+), 12 deletions(-)
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 9267291..1c45b6a 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c@@ -2439,7 +2439,7 @@ struct devname_cache { char devname[BDEVNAME_SIZE]; }; #define CACHE_SIZE_BITS 6 -static struct devname_cache *devcache[1 << CACHE_SIZE_BITS]; +static struct devname_cache __rcu *devcache[1 << CACHE_SIZE_BITS]; static DEFINE_SPINLOCK(devname_cache_lock); const char *jbd2_dev_to_name(dev_t device)
@@ -2447,24 +2447,25 @@ const char *jbd2_dev_to_name(dev_t device) int i = hash_32(device, CACHE_SIZE_BITS); char *ret; struct block_device *bd; - static struct devname_cache *new_dev; + static struct devname_cache *cache; rcu_read_lock(); - if (devcache[i] && devcache[i]->device == device) { - ret = devcache[i]->devname; + cache = rcu_dereference(devcache[i]); + if (cache && cache->device == device) { + ret = cache->devname; rcu_read_unlock(); return ret; } rcu_read_unlock(); - new_dev = kmalloc(sizeof(struct devname_cache), GFP_KERNEL); - if (!new_dev) + cache = kmalloc(sizeof(struct devname_cache), GFP_KERNEL); + if (!cache) return "NODEV-ALLOCFAILURE"; /* Something non-NULL */ bd = bdget(device); spin_lock(&devname_cache_lock); if (devcache[i]) { if (devcache[i]->device == device) { - kfree(new_dev); + kfree(cache); bdput(bd); ret = devcache[i]->devname; spin_unlock(&devname_cache_lock);
@@ -2472,14 +2473,14 @@ const char *jbd2_dev_to_name(dev_t device) } kfree_rcu(devcache[i], rcu); } - devcache[i] = new_dev; - devcache[i]->device = device; + cache->device = device; if (bd) { - bdevname(bd, devcache[i]->devname); + bdevname(bd, cache->devname); bdput(bd); } else - __bdevname(device, devcache[i]->devname); - ret = devcache[i]->devname; + __bdevname(device, cache->devname); + rcu_assign_pointer(devcache[i], cache); + ret = cache->devname; spin_unlock(&devname_cache_lock); return ret; }
--
1.7.4.4