Btrfs: use rcu to protect device->name
Al pointed out that we can just toss out the old name on a device and add a
new one arbitrarily, so anybody who uses device->name in printk could
possibly use free'd memory. Instead of adding locking around all of this he
suggested doing it with RCU, so I've introduced a struct rcu_string that
does just that and have gone through and protected all accesses to
device->name that aren't under the uuid_mutex with rcu_read_lock(). This
protects us and I will use it for dealing with removing the device that we
used to mount the file system in a later patch. Thanks,
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <josef@redhat.com>
diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index 9cebb1f..da6e936 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -93,6 +93,7 @@
#include "print-tree.h"
#include "locking.h"
#include "check-integrity.h"
+#include "rcu-string.h"
#define BTRFSIC_BLOCK_HASHTABLE_SIZE 0x10000
#define BTRFSIC_BLOCK_LINK_HASHTABLE_SIZE 0x10000
@@ -843,13 +844,14 @@
superblock_tmp->never_written = 0;
superblock_tmp->mirror_num = 1 + superblock_mirror_num;
if (state->print_mask & BTRFSIC_PRINT_MASK_SUPERBLOCK_WRITE)
- printk(KERN_INFO "New initial S-block (bdev %p, %s)"
- " @%llu (%s/%llu/%d)\n",
- superblock_bdev, device->name,
- (unsigned long long)dev_bytenr,
- dev_state->name,
- (unsigned long long)dev_bytenr,
- superblock_mirror_num);
+ printk_in_rcu(KERN_INFO "New initial S-block (bdev %p, %s)"
+ " @%llu (%s/%llu/%d)\n",
+ superblock_bdev,
+ rcu_str_deref(device->name),
+ (unsigned long long)dev_bytenr,
+ dev_state->name,
+ (unsigned long long)dev_bytenr,
+ superblock_mirror_num);
list_add(&superblock_tmp->all_blocks_node,
&state->all_blocks_list);
btrfsic_block_hashtable_add(superblock_tmp,
