svn commit: r346990 - head/sys/vm
Konstantin Belousov
kib at FreeBSD.org
Wed May 1 13:15:08 UTC 2019
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 <dougm at rice.edu>, 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;
}
/*
More information about the svn-src-all
mailing list