Date: Thu, 5 Sep 2013 12:54:40 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r255244 - head/sys/vm Message-ID: <201309051254.r85CseR5014796@svn.freebsd.org>
next in thread | raw e-mail | index | archive | help
Author: kib Date: Thu Sep 5 12:54:40 2013 New Revision: 255244 URL: http://svnweb.freebsd.org/changeset/base/255244 Log: 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 Modified: head/sys/vm/vm_page.c Modified: head/sys/vm/vm_page.c ============================================================================== --- head/sys/vm/vm_page.c Thu Sep 5 12:35:23 2013 (r255243) +++ head/sys/vm/vm_page.c Thu Sep 5 12:54:40 2013 (r255244) @@ -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); + } } /*
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201309051254.r85CseR5014796>