Commit f84adf49 authored by Konrad Rzeszutek Wilk's avatar Konrad Rzeszutek Wilk
Browse files

xen-blkfront: drop the use of llist_for_each_entry_safe



Replace llist_for_each_entry_safe with a while loop.

llist_for_each_entry_safe can trigger a bug in GCC 4.1, so it's best
to remove it and use a while loop and do the deletion manually.

Specifically this bug can be triggered by hot-unplugging a disk, either
by doing xm block-detach or by save/restore cycle.

BUG: unable to handle kernel paging request at fffffffffffffff0
IP: [<ffffffffa0047223>] blkif_free+0x63/0x130 [xen_blkfront]
The crash call trace is:
	...
bad_area_nosemaphore+0x13/0x20
do_page_fault+0x25e/0x4b0
page_fault+0x25/0x30
? blkif_free+0x63/0x130 [xen_blkfront]
blkfront_resume+0x46/0xa0 [xen_blkfront]
xenbus_dev_resume+0x6c/0x140
pm_op+0x192/0x1b0
device_resume+0x82/0x1e0
dpm_resume+0xc9/0x1a0
dpm_resume_end+0x15/0x30
do_suspend+0x117/0x1e0

When drilling down to the assembler code, on newer GCC it does
.L29:
        cmpq    $-16, %r12      #, persistent_gnt check
        je      .L30    	#, out of the loop
.L25:
	... code in the loop
        testq   %r13, %r13      # n
        je      .L29    	#, back to the top of the loop
        cmpq    $-16, %r12      #, persistent_gnt check
        movq    16(%r12), %r13  # <variable>.node.next, n
        jne     .L25    	#,	back to the top of the loop
.L30:

While on GCC 4.1, it is:
L78:
	... code in the loop
	testq   %r13, %r13      # n
        je      .L78    #,	back to the top of the loop
        movq    16(%rbx), %r13  # <variable>.node.next, n
        jmp     .L78    #,	back to the top of the loop

Which basically means that the exit loop condition instead of
being:

	&(pos)->member != NULL;

is:
	;

which makes the loop unbound.

Since xen-blkfront is the only user of the llist_for_each_entry_safe
macro remove it from llist.h.

Orabug: 16263164
CC: stable@vger.kernel.org
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 01c681d4
......@@ -791,7 +791,7 @@ static void blkif_restart_queue(struct work_struct *work)
static void blkif_free(struct blkfront_info *info, int suspend)
{
struct llist_node *all_gnts;
struct grant *persistent_gnt;
struct grant *persistent_gnt, *tmp;
struct llist_node *n;
/* Prevent new requests being issued until we fix things up. */
......@@ -805,10 +805,17 @@ 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_safe(persistent_gnt, n, all_gnts, node) {
persistent_gnt = llist_entry(all_gnts, typeof(*(persistent_gnt)), node);
while (persistent_gnt) {
gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
__free_page(pfn_to_page(persistent_gnt->pfn));
kfree(persistent_gnt);
tmp = persistent_gnt;
n = persistent_gnt->node.next;
if (n)
persistent_gnt = llist_entry(n, typeof(*(persistent_gnt)), node);
else
persistent_gnt = NULL;
kfree(tmp);
}
info->persistent_gnts_c = 0;
}
......
......@@ -124,31 +124,6 @@ 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
......
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