Date: Sun, 26 Dec 2010 13:10:12 GMT From: dfilter@FreeBSD.ORG (dfilter service) To: freebsd-xen@FreeBSD.org Subject: Re: kern/140313: commit references a PR Message-ID: <201012261310.oBQDACZ5010337@freefall.freebsd.org>
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The following reply was made to PR kern/140313; it has been noted by GNATS. From: dfilter@FreeBSD.ORG (dfilter service) To: bug-followup@FreeBSD.org Cc: Subject: Re: kern/140313: commit references a PR Date: Sun, 26 Dec 2010 13:05:48 +0000 (UTC) Author: cperciva Date: Sun Dec 26 13:05:43 2010 New Revision: 216703 URL: http://svn.freebsd.org/changeset/base/216703 Log: Lock the vm page queue mutex in pmap_pte_release around the call to PMAP_SET_VA; this fixes a mutex-not-held panic when a process which called mlock(2) exits, and parallels a change made in pmap_pte 10 months ago (svn r204160). Note: The locking in this code is utterly broken. We should not be using the VM page queue mutex to protect the queue of pending Xen page mapping hypervisor calls. Even if it made sense to do so, this commit and r204160 introduce LORs between the vm page queue mutex and PMAP2mutex. (However, a possible deadlock is better than a guaranteed panic, and this change will hopefully make life easier for whoever fixes the Xen pmap locking in the future.) PR: kern/140313 MFC after: 3 days Modified: head/sys/i386/xen/pmap.c Modified: head/sys/i386/xen/pmap.c ============================================================================== --- head/sys/i386/xen/pmap.c Sun Dec 26 01:42:52 2010 (r216702) +++ head/sys/i386/xen/pmap.c Sun Dec 26 13:05:43 2010 (r216703) @@ -1015,7 +1015,9 @@ pmap_pte_release(pt_entry_t *pte) if ((pt_entry_t *)((vm_offset_t)pte & ~PAGE_MASK) == PADDR2) { CTR1(KTR_PMAP, "pmap_pte_release: pte=0x%jx", *PMAP2); + vm_page_lock_queues(); PT_SET_VA(PMAP2, 0, TRUE); + vm_page_unlock_queues(); mtx_unlock(&PMAP2mutex); } } _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscribe@freebsd.org"
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