In a non-uml kernel a get_user() when current->mm is NULL (kernel thread, or
userspace process being torn down) returns error. In uml it SEGVs. The bug is
that handle_page_fault() does not check for NULL before using mm. The
trivial attached patch fixes this.
-Nicolas Dade
--- linux-2.6.21.2/arch/um/kernel/trap.c.orig 2007-05-24 02:22:42.000000000
-0700
+++ linux-2.6.21.2/arch/um/kernel/trap.c 2007-05-24 02:23:45.000000000
-0700
@@ -51,6 +51,9 @@
* fail. */
if (in_atomic())
goto out_nosemaphore;
+ /* If we have no user-space just fail */
+ if (!mm)
+ goto out_nosemaphore;
down_read(&mm->mmap_sem);
vma = find_vma(mm, address);
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