Date: Sat, 20 Nov 2010 04:54:58 +0000 (UTC) From: Ryan Stone <rstone@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-8@freebsd.org Subject: svn commit: r215551 - stable/8/sys/vm Message-ID: <201011200454.oAK4swPc000417@svn.freebsd.org>
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Author: rstone Date: Sat Nov 20 04:54:58 2010 New Revision: 215551 URL: http://svn.freebsd.org/changeset/base/215551 Log: MFC r212281 and 212282 In munmap() downgrade the vm_map_lock to a read lock before taking a read lock on the pmc-sx lock. This prevents a deadlock with pmc_log_process_mappings, which has an exclusive lock on pmc-sx and tries to get a read lock on a vm_map. Downgrading the vm_map_lock in munmap allows pmc_log_process_mappings to continue, preventing the deadlock. Without this change I could cause a deadlock on a multicore 8.1-RELEASE system by having one thread constantly mmap'ing and then munmap'ing a PROT_EXEC mapping in a loop while I repeatedly invoked and stopped pmcstat in system-wide sampling mode. Approved by: emaste (mentor) Modified: stable/8/sys/vm/vm_mmap.c Directory Properties: stable/8/sys/ (props changed) stable/8/sys/amd64/include/xen/ (props changed) stable/8/sys/cddl/contrib/opensolaris/ (props changed) stable/8/sys/contrib/dev/acpica/ (props changed) stable/8/sys/contrib/pf/ (props changed) stable/8/sys/dev/xen/xenpci/ (props changed) Modified: stable/8/sys/vm/vm_mmap.c ============================================================================== --- stable/8/sys/vm/vm_mmap.c Fri Nov 19 22:25:32 2010 (r215550) +++ stable/8/sys/vm/vm_mmap.c Sat Nov 20 04:54:58 2010 (r215551) @@ -577,6 +577,7 @@ munmap(td, uap) * Inform hwpmc if the address range being unmapped contains * an executable region. */ + pkm.pm_address = (uintptr_t) NULL; if (vm_map_lookup_entry(map, addr, &entry)) { for (; entry != &map->header && entry->start < addr + size; @@ -585,16 +586,23 @@ munmap(td, uap) entry->end, VM_PROT_EXECUTE) == TRUE) { pkm.pm_address = (uintptr_t) addr; pkm.pm_size = (size_t) size; - PMC_CALL_HOOK(td, PMC_FN_MUNMAP, - (void *) &pkm); break; } } } #endif - /* returns nothing but KERN_SUCCESS anyway */ vm_map_delete(map, addr, addr + size); + +#ifdef HWPMC_HOOKS + /* downgrade the lock to prevent a LOR with the pmc-sx lock */ + vm_map_lock_downgrade(map); + if (pkm.pm_address != (uintptr_t) NULL) + PMC_CALL_HOOK(td, PMC_FN_MUNMAP, (void *) &pkm); + vm_map_unlock_read(map); +#else vm_map_unlock(map); +#endif + /* vm_map_delete returns nothing but KERN_SUCCESS anyway */ return (0); }
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