Author: kib Date: Wed May 1 13:15:06 2019 New Revision: 346990 URL: https://svnweb.freebsd.org/changeset/base/346990
Log: Fix another race between vm_map_protect() and vm_map_wire(). vm_map_wire() increments entry->wire_count, after that it drops the map lock both for faulting in the entry' pages, and for marking next entry in the requested region as IN_TRANSITION. Only after all entries are faulted in, MAP_ENTRY_USER_WIRE flag is set. This makes it possible for vm_map_protect() to run while other entry' MAP_ENTRY_IN_TRANSITION flag is handled, and vm_map_busy() lock does not prevent it. In particular, if the call to vm_map_protect() adds VM_PROT_WRITE to CoW entry, it would fail to call vm_fault_copy_entry(). There are at least two consequences of the race: the top object in the shadow chain is not populated with writeable pages, and second, the entry eventually get contradictory flags MAP_ENTRY_NEEDS_COPY | MAP_ENTRY_USER_WIRED with VM_PROT_WRITE set. Handle it by waiting for all MAP_ENTRY_IN_TRANSITION flags to go away in vm_map_protect(), which does not drop map lock afterwards. Note that vm_map_busy_wait() is left as is. Reported and tested by: pho (previous version) Reviewed by: Doug Moore <[email protected]>, markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D20091 Modified: head/sys/vm/vm_map.c Modified: head/sys/vm/vm_map.c ============================================================================== --- head/sys/vm/vm_map.c Wed May 1 13:00:33 2019 (r346989) +++ head/sys/vm/vm_map.c Wed May 1 13:15:06 2019 (r346990) @@ -2347,7 +2347,7 @@ int vm_map_protect(vm_map_t map, vm_offset_t start, vm_offset_t end, vm_prot_t new_prot, boolean_t set_max) { - vm_map_entry_t current, entry; + vm_map_entry_t current, entry, in_tran; vm_object_t obj; struct ucred *cred; vm_prot_t old_prot; @@ -2355,6 +2355,8 @@ vm_map_protect(vm_map_t map, vm_offset_t start, vm_off if (start == end) return (KERN_SUCCESS); +again: + in_tran = NULL; vm_map_lock(map); /* @@ -2387,6 +2389,22 @@ vm_map_protect(vm_map_t map, vm_offset_t start, vm_off vm_map_unlock(map); return (KERN_PROTECTION_FAILURE); } + if ((entry->eflags & MAP_ENTRY_IN_TRANSITION) != 0) + in_tran = entry; + } + + /* + * Postpone the operation until all in transition map entries + * are stabilized. In-transition entry might already have its + * pages wired and wired_count incremented, but + * MAP_ENTRY_USER_WIRED flag not yet set, and visible to other + * threads because the map lock is dropped. In this case we + * would miss our call to vm_fault_copy_entry(). + */ + if (in_tran != NULL) { + in_tran->eflags |= MAP_ENTRY_NEEDS_WAKEUP; + vm_map_unlock_and_wait(map, 0); + goto again; } /* _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "[email protected]"
