Merge to Fedora kernel-2.6.7-1.492

[linux-2.6.git] / arch / ppc64 / mm / fault.c

diff --git a/arch/ppc64/mm/fault.c b/arch/ppc64/mm/fault.c
index 72eba98..71c1598 100644 (file)
--- a/arch/ppc64/mm/fault.c
+++ b/arch/ppc64/mm/fault.c
@@ -119,7 +119,28 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
                die("Weird page fault", regs, SIGSEGV);
        }
 
-       down_read(&mm->mmap_sem);
+       /* When running in the kernel we expect faults to occur only to
+        * addresses in user space.  All other faults represent errors in the
+        * kernel and should generate an OOPS.  Unfortunatly, in the case of an
+        * erroneous fault occuring in a code path which already holds mmap_sem
+        * we will deadlock attempting to validate the fault against the
+        * address space.  Luckily the kernel only validly references user
+        * space from well defined areas of code, which are listed in the
+        * exceptions table.
+        *
+        * As the vast majority of faults will be valid we will only perform
+        * the source reference check when there is a possibilty of a deadlock.
+        * Attempt to lock the address space, if we cannot we then validate the
+        * source.  If this is invalid we can skip the address space check,
+        * thus avoiding the deadlock.
+        */
+       if (!down_read_trylock(&mm->mmap_sem)) {
+               if (!user_mode(regs) && !search_exception_tables(regs->nip))
+                       goto bad_area_nosemaphore;
+
+               down_read(&mm->mmap_sem);
+       }
+
        vma = find_vma(mm, address);
        if (!vma)
                goto bad_area;
@@ -209,12 +230,13 @@ good_area:
 bad_area:
        up_read(&mm->mmap_sem);
 
+bad_area_nosemaphore:
        /* User mode accesses cause a SIGSEGV */
        if (user_mode(regs)) {
                info.si_signo = SIGSEGV;
                info.si_errno = 0;
                info.si_code = code;
-               info.si_addr = (void *) address;
+               info.si_addr = (void __user *) address;
                force_sig_info(SIGSEGV, &info, current);
                return 0;
        }
@@ -243,7 +265,7 @@ do_sigbus:
                info.si_signo = SIGBUS;
                info.si_errno = 0;
                info.si_code = BUS_ADRERR;
-               info.si_addr = (void *)address;
+               info.si_addr = (void __user *)address;
                force_sig_info(SIGBUS, &info, current);
                return 0;
        }