From 0dd3ce30eb28360680a5d3776ec8eb0bf6848bfb Mon Sep 17 00:00:00 2001 From: rstone Date: Tue, 7 Sep 2010 00:23:45 +0000 Subject: 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. Reviewed by: fabient Approved by: emaste (mentor) MFC after: 2 weeks --- sys/vm/vm_mmap.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) (limited to 'sys') diff --git a/sys/vm/vm_mmap.c b/sys/vm/vm_mmap.c index 2071cc7..c912678 100644 --- a/sys/vm/vm_mmap.c +++ b/sys/vm/vm_mmap.c @@ -579,6 +579,7 @@ 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; @@ -587,16 +588,23 @@ 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) 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); } -- cgit v1.1