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llist/xen-blkfront: implement safe version of llist_for_each_entry 

Implement a safe version of llist_for_each_entry, and use it in
blkif_free. Previously grants where freed while iterating the list,
which lead to dereferences when trying to fetch the next item.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by:  Andrew Morton <akpm@linux-foundation.org>
[v2: Move the llist_for_each_entry_safe in llist.h]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Roger Pau Monne 2012-12-04 15:21:53 +01:00 committed by Konrad Rzeszutek Wilk
parent 7dc341175a
commit ebb351cf78
2 changed files with 27 additions and 1 deletions
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3
drivers/block/xen-blkfront.c
View File

@ -792,6 +792,7 @@ static void blkif_free(struct blkfront_info *info, int suspend)
{
struct llist_node *all_gnts;
struct grant *persistent_gnt;
struct llist_node *n;
/* Prevent new requests being issued until we fix things up. */
spin_lock_irq(&info->io_lock);
@ -804,7 +805,7 @@ static void blkif_free(struct blkfront_info *info, int suspend)
/* Remove all persistent grants */
if (info->persistent_gnts_c) {
all_gnts = llist_del_all(&info->persistent_gnts);
llist_for_each_entry(persistent_gnt, all_gnts, node) {
llist_for_each_entry_safe(persistent_gnt, n, all_gnts, node) {
gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
__free_page(pfn_to_page(persistent_gnt->pfn));
kfree(persistent_gnt);

25
include/linux/llist.h
View File

@ -124,6 +124,31 @@ static inline void init_llist_head(struct llist_head *list)
&(pos)->member != NULL; \
(pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
/**
* llist_for_each_entry_safe - iterate safely against remove over some entries
* of lock-less list of given type.
* @pos: the type * to use as a loop cursor.
* @n: another type * to use as a temporary storage.
* @node: the fist entry of deleted list entries.
* @member: the name of the llist_node with the struct.
*
* In general, some entries of the lock-less list can be traversed
* safely only after being removed from list, so start with an entry
* instead of list head. This variant allows removal of entries
* as we iterate.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
* you want to traverse from the oldest to the newest, you must
* reverse the order by yourself before traversing.
*/
#define llist_for_each_entry_safe(pos, n, node, member) \
for ((pos) = llist_entry((node), typeof(*(pos)), member), \
(n) = (pos)->member.next; \
&(pos)->member != NULL; \
(pos) = llist_entry(n, typeof(*(pos)), member), \
(n) = (&(pos)->member != NULL) ? (pos)->member.next : NULL)
/**
* llist_empty - tests whether a lock-less list is empty
* @head: the list to test