Author: kib Date: Tue Oct 11 18:09:37 2016 New Revision: 307064 URL: https://svnweb.freebsd.org/changeset/base/307064
Log: When downgrading exclusively busied page to shared-busy state, wakeup waiters. Otherwise, owners of the shared-busy state are left blocked and might get into a deadlock. Note that the vm_page_busy_downgrade() function is not used in the tree right now. Reported and tested by: pho (previous version) Reviewed by: alc, markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D8195 Modified: head/sys/vm/vm_page.c Modified: head/sys/vm/vm_page.c ============================================================================== --- head/sys/vm/vm_page.c Tue Oct 11 17:47:54 2016 (r307063) +++ head/sys/vm/vm_page.c Tue Oct 11 18:09:37 2016 (r307064) @@ -655,15 +655,26 @@ void vm_page_busy_downgrade(vm_page_t m) { u_int x; + bool locked; vm_page_assert_xbusied(m); + locked = mtx_owned(vm_page_lockptr(m)); for (;;) { x = m->busy_lock; x &= VPB_BIT_WAITERS; + if (x != 0 && !locked) + vm_page_lock(m); if (atomic_cmpset_rel_int(&m->busy_lock, - VPB_SINGLE_EXCLUSIVER | x, VPB_SHARERS_WORD(1) | x)) + VPB_SINGLE_EXCLUSIVER | x, VPB_SHARERS_WORD(1))) break; + if (x != 0 && !locked) + vm_page_unlock(m); + } + if (x != 0) { + wakeup(m); + if (!locked) + vm_page_unlock(m); } } _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
