On Wed, Mar 30, 2005 at 03:56:19PM -0800, dean gaudet wrote:
> having looked at the oops below and studied the code a bit more i think
> that the safest thing to do for 2.4.x to fix this race condition is to get
> rid of the unsafe promote-to-front hash list traversal. i considered
> other fixes (such as a separate spinlock for just the hash list, or a
> small array of them to give some amount of concurrency) ... but in the
> interests of stability the following patch seems the most appropriate.
>
> besides... nobody has responded to my mail, so perhaps proposing this
> patch to marcelo will cause folks to wake up and object :)
>
> -dean
>
> Signed-off-by: dean gaudet <dean@arctic.org>
>
> --- linux-2.4.29/drivers/md/lvm-snap.c.orig 2005-03-25 22:03:43.000000000 -0800
> +++ linux-2.4.29/drivers/md/lvm-snap.c 2005-03-30 01:46:17.000000000 -0800
> @@ -119,7 +119,6 @@ static inline lv_block_exception_t *lvm_
> unsigned long mask = lv->lv_snapshot_hash_mask;
> int chunk_size = lv->lv_chunk_size;
> lv_block_exception_t *ret;
> - int i = 0;
>
> hash_table =
> &hash_table[hashfn(org_dev, org_start, mask, chunk_size)];
> @@ -132,15 +131,9 @@ static inline lv_block_exception_t *lvm_
> exception = list_entry(next, lv_block_exception_t, hash);
> if (exception->rsector_org == org_start &&
> exception->rdev_org == org_dev) {
> - if (i) {
> - /* fun, isn't it? :) */
> - list_del(next);
> - list_add(next, hash_table);
> - }
> ret = exception;
> break;
> }
> - i++;
> }
> return ret;
> }
Hi dean,
The hash table write is not performed anymore (ie your suggestion is already in).
D 1.15 05/01/26 13:01:33-02:00 mauelshagen@redhat.com[marcelo] 16 15 0/7/750
P drivers/md/lvm-snap.c
C fix panics while backing up LVM snapshots
===== lvm-snap.c 1.14 vs 1.15 =====
--- 1.14/drivers/md/lvm-snap.c 2004-03-13 02:25:25 -03:00
+++ 1.15/drivers/md/lvm-snap.c 2005-01-26 13:01:33 -02:00
@@ -119,7 +119,6 @@
unsigned long mask = lv->lv_snapshot_hash_mask;
int chunk_size = lv->lv_chunk_size;
lv_block_exception_t *ret;
- int i = 0;
hash_table =
&hash_table[hashfn(org_dev, org_start, mask, chunk_size)];
@@ -132,15 +131,9 @@
exception = list_entry(next, lv_block_exception_t, hash);
if (exception->rsector_org == org_start &&
exception->rdev_org == org_dev) {
- if (i) {
- /* fun, isn't it? :) */
- list_del(next);
- list_add(next, hash_table);
- }
ret = exception;
break;
}
- i++;
}
return ret;
}
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