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Btrfs: use rcu to protect device->name

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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>
This commit is contained in:
Josef Bacik
2012-06-04 14:03:51 -04:00
committed by Chris Mason
parent 17ca04aff7
commit 606686eeac
8 changed files with 162 additions and 64 deletions
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10
fs/btrfs/disk-io.c
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@@ -44,6 +44,7 @@
#include "free-space-cache.h"
#include "inode-map.h"
#include "check-integrity.h"
#include "rcu-string.h"
static struct extent_io_ops btree_extent_io_ops;
static void end_workqueue_fn(struct btrfs_work *work);
@@ -2575,8 +2576,9 @@ static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
struct btrfs_device *device = (struct btrfs_device *)
bh->b_private;
printk_ratelimited(KERN_WARNING "lost page write due to "
"I/O error on %s\n", device->name);
printk_ratelimited_in_rcu(KERN_WARNING "lost page write due to "
"I/O error on %s\n",
rcu_str_deref(device->name));
/* note, we dont' set_buffer_write_io_error because we have
* our own ways of dealing with the IO errors
*/
@@ -2749,8 +2751,8 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
wait_for_completion(&device->flush_wait);
if (bio_flagged(bio, BIO_EOPNOTSUPP)) {
printk("btrfs: disabling barriers on dev %s\n",
device->name);
printk_in_rcu("btrfs: disabling barriers on dev %s\n",
rcu_str_deref(device->name));
device->nobarriers = 1;
}
if (!bio_flagged(bio, BIO_UPTODATE)) {