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In swp_pager_meta_build(), handle a race with other thread allocating

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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
This commit is contained in:
Konstantin Belousov 2017-09-06 16:16:11 +00:00
parent badd2a3546
commit eed99cb81b
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=323224
1 changed files with 18 additions and 1 deletions
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19
sys/vm/swap_pager.c
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@ -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 pindex, daddr_t swapblk)
} 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 pindex, daddr_t swapblk)
} 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;