Author: kib
Date: Wed Sep 6 16:16:11 2017
New Revision: 323224
URL: https://svnweb.freebsd.org/changeset/base/323224
Log:
In swp_pager_meta_build(), handle a race with other thread allocating
swapblk for our index while we dropped the object lock.
Noted by: jeff
Reviewed by: alc, markj
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Modified:
head/sys/vm/swap_pager.c
Modified: head/sys/vm/swap_pager.c
==============================================================================
--- head/sys/vm/swap_pager.c Wed Sep 6 15:33:23 2017 (r323223)
+++ head/sys/vm/swap_pager.c Wed Sep 6 16:16:11 2017 (r323224)
@@ -1726,7 +1726,7 @@ static void
swp_pager_meta_build(vm_object_t object, vm_pindex_t pindex, daddr_t swapblk)
{
static volatile int swblk_zone_exhausted, swpctrie_zone_exhausted;
- struct swblk *sb;
+ struct swblk *sb, *sb1;
vm_pindex_t modpi, rdpi;
int error, i;
@@ -1776,6 +1776,15 @@ swp_pager_meta_build(vm_object_t object, vm_pindex_t p
} else
VM_WAIT;
VM_OBJECT_WLOCK(object);
+ sb = SWAP_PCTRIE_LOOKUP(&object->un_pager.swp.swp_blks,
+ rdpi);
+ if (sb != NULL)
+ /*
+ * Somebody swapped out a nearby page,
+ * allocating swblk at the rdpi index,
+ * while we dropped the object lock.
+ */
+ goto allocated;
}
for (;;) {
error = SWAP_PCTRIE_INSERT(
@@ -1797,8 +1806,16 @@ swp_pager_meta_build(vm_object_t object, vm_pindex_t p
} else
VM_WAIT;
VM_OBJECT_WLOCK(object);
+ sb1 = SWAP_PCTRIE_LOOKUP(&object->un_pager.swp.swp_blks,
+ rdpi);
+ if (sb1 != NULL) {
+ uma_zfree(swblk_zone, sb);
+ sb = sb1;
+ goto allocated;
+ }
}
}
+allocated:
MPASS(sb->p == rdpi);
modpi = pindex % SWAP_META_PAGES;
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