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Commit 2d910543 authored by Roger Pau Monne's avatar Roger Pau Monne Committed by Konrad Rzeszutek Wilk
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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: default avatarRoger Pau Monné <roger.pau@citrix.com>
Reported-by: default avatarTom O'Neill <toneill@vmem.com>
Reported-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 8e3f8755

drivers/block/xen-blkback/blkback.c

+14 −10
Original line number Diff line number Diff line
@@ -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;