Roger Pau Monne
2013-Jun-21 10:56 UTC
[PATCH 1/4] xen-blkback: workaround compiler bug in gcc 4.1
The code generat with gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-54)
creates an unbound loop for the second foreach_grant_safe loop in
purge_persistent_gnt.
The workaround is to avoid having this second loop and instead
perform all the work inside the first loop by adding a new variable,
clean_used, that will be set when all the desired persistent grants
have been removed and we need to iterate over the remaining ones to
remove the WAS_ACTIVE flag.
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reported-by: Tom O'Neill <toneill@vmem.com>
Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
drivers/block/xen-blkback/blkback.c | 24 ++++++++++++++----------
1 files changed, 14 insertions(+), 10 deletions(-)
diff --git a/drivers/block/xen-blkback/blkback.c
b/drivers/block/xen-blkback/blkback.c
index 4119bcd..d622d86 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -341,7 +341,7 @@ static void purge_persistent_gnt(struct xen_blkif *blkif)
struct persistent_gnt *persistent_gnt;
struct rb_node *n;
unsigned int num_clean, total;
- bool scan_used = false;
+ bool scan_used = false, clean_used = false;
struct rb_root *root;
if (blkif->persistent_gnt_c < xen_blkif_max_pgrants ||
@@ -358,9 +358,8 @@ static void purge_persistent_gnt(struct xen_blkif *blkif)
num_clean = (xen_blkif_max_pgrants / 100) * LRU_PERCENT_CLEAN;
num_clean = blkif->persistent_gnt_c - xen_blkif_max_pgrants + num_clean;
num_clean = min(blkif->persistent_gnt_c, num_clean);
- if (num_clean >
- (blkif->persistent_gnt_c -
- atomic_read(&blkif->persistent_gnt_in_use)))
+ if ((num_clean == 0) ||
+ (num_clean > (blkif->persistent_gnt_c -
atomic_read(&blkif->persistent_gnt_in_use))))
return;
/*
@@ -383,6 +382,11 @@ purge_list:
BUG_ON(persistent_gnt->handle = BLKBACK_INVALID_HANDLE);
+ if (clean_used) {
+ clear_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags);
+ continue;
+ }
+
if (test_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags))
continue;
if (!scan_used &&
@@ -400,18 +404,18 @@ purge_list:
* grants that were used since last purge in order to cope
* with the requested num
*/
- if (!scan_used) {
+ if (!scan_used && !clean_used) {
pr_debug(DRV_PFX "Still missing %u purged frames\n", num_clean);
scan_used = true;
goto purge_list;
}
finished:
- /* Remove the "used" flag from all the persistent grants */
- foreach_grant_safe(persistent_gnt, n, root, node) {
- BUG_ON(persistent_gnt->handle =- BLKBACK_INVALID_HANDLE);
- clear_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags);
+ if (!clean_used) {
+ pr_debug(DRV_PFX "Finished scanning for grants to clean, removing used
flag\n");
+ clean_used = true;
+ goto purge_list;
}
+
blkif->persistent_gnt_c -= (total - num_clean);
blkif->vbd.overflow_max_grants = 0;
--
1.7.7.5 (Apple Git-26)
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