X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=arch%2Fppc64%2Fmm%2Ffault.c;h=71c159841de5683e0ed3c59588b5721bb12d58d3;hb=70790a4b5cd6c0291e5b1a2836e2832d46036ac6;hp=72eba98f4dd8eeb412bd6f7d7ada0a4790983d3a;hpb=413ba3004a4036bb5d6e52d2faa2b19cb13561dc;p=linux-2.6.git

diff --git a/arch/ppc64/mm/fault.c b/arch/ppc64/mm/fault.c
index 72eba98f4..71c159841 100644
--- 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;
 	}