[PATCH] __vm_enough_memory() signedness fix
We have found what seems to be a small bug in __vm_enough_memory() when
sysctl_overcommit_memory is set to OVERCOMMIT_NEVER.
When this bug occurs the systems fails to boot, with /sbin/init whining
about fork() returning ENOMEM.
We hunted down the problem to this:
The deferred update mecanism used in vm_acct_memory(), on a SMP system,
allows the vm_committed_space counter to have a negative value.
This should not be a problem since this counter is known to be inaccurate.
But in __vm_enough_memory() this counter is compared to the `allowed'
variable, which is an unsigned long. This comparison is broken since it
will consider the negative values of vm_committed_space to be huge positive
values, resulting in a memory allocation failure.
Signed-off-by: <Jean-Marc.Saffroy@ext.bull.net>
Signed-off-by: <Simon.Derr@bull.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/nommu.c b/mm/nommu.c
index ce74452..fd4e8df 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1167,7 +1167,11 @@
leave 3% of the size of this process for other processes */
allowed -= current->mm->total_vm / 32;
- if (atomic_read(&vm_committed_space) < allowed)
+ /*
+ * cast `allowed' as a signed long because vm_committed_space
+ * sometimes has a negative value
+ */
+ if (atomic_read(&vm_committed_space) < (long)allowed)
return 0;
vm_unacct_memory(pages);