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| author | kib <kib@FreeBSD.org> | 2013-09-05 12:54:40 +0000 |
|---|---|---|
| committer | kib <kib@FreeBSD.org> | 2013-09-05 12:54:40 +0000 |
| commit | 7ab18d4990d80767c250514df82b25bd076c5801 (patch) | |
| tree | 138dc3860ef9530acb37af4e45319255e4607094 /sys/vm/vm_page.c | |
| parent | 795da63f42e0a9f2beb0ea81351fc839f169fa6e (diff) | |
| download | FreeBSD-src-7ab18d4990d80767c250514df82b25bd076c5801.zip FreeBSD-src-7ab18d4990d80767c250514df82b25bd076c5801.tar.gz | |
The vm_page_trysbusy() should not fail when shared busy counter or
VPB_BIT_WAITERS flag were changed between reading of busy_lock and the
cas. The vm_page_sbusy(), which is the only user of
vm_page_trysbusy() in the tree, panics on the failure, which in these
cases is transient and do not mean that the current page state
prevents sbusying.
Retry the operation inside vm_page_trysbusy() if cas failed, only
return a failure when VPB_BIT_SHARED is cleared.
Reported and tested by: pho
Reviewed by: attilio
Sponsored by: The FreeBSD Foundation
Diffstat (limited to 'sys/vm/vm_page.c')
| -rw-r--r-- | sys/vm/vm_page.c | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c index 7b4b57c..53ffc72 100644 --- a/sys/vm/vm_page.c +++ b/sys/vm/vm_page.c @@ -602,9 +602,13 @@ vm_page_trysbusy(vm_page_t m) { u_int x; - x = m->busy_lock; - return ((x & VPB_BIT_SHARED) != 0 && - atomic_cmpset_acq_int(&m->busy_lock, x, x + VPB_ONE_SHARER)); + for (;;) { + x = m->busy_lock; + if ((x & VPB_BIT_SHARED) == 0) + return (0); + if (atomic_cmpset_acq_int(&m->busy_lock, x, x + VPB_ONE_SHARER)) + return (1); + } } /* |
