rpms/kernel/devel linux-2.6-mm-pagefault-enable-ints.patch, NONE, 1.1 kernel.spec, 1.1117, 1.1118

[Dave Jones]

Author: davej

Update of /cvs/pkgs/rpms/kernel/devel
In directory cvs1.fedora.phx.redhat.com:/tmp/cvs-serv2520

Modified Files:
	kernel.spec 
Added Files:
	linux-2.6-mm-pagefault-enable-ints.patch 
Log Message:
x86/mm: do not trigger a kernel warning if user-space disables interrupts and generates a page fault

linux-2.6-mm-pagefault-enable-ints.patch:

--- NEW FILE linux-2.6-mm-pagefault-enable-ints.patch ---
commit 891cffbd6bcba26409869c19c07ecd4bfc0c2460
Author: Linus Torvalds <torvalds at linux-foundation.org>
Date:   Sun Oct 12 13:16:12 2008 -0700

    x86/mm: do not trigger a kernel warning if user-space disables interrupts and generates a page fault
    
    Arjan reported a spike in the following bug pattern in v2.6.27:
    
       http://www.kerneloops.org/searchweek.php?search=lock_page
    
    which happens because hwclock started triggering warnings due to
    a (correct) might_sleep() check in the MM code.
    
    The warning occurs because hwclock uses this dubious sequence of
    code to run "atomic" code:
    
      static unsigned long
      atomic(const char *name, unsigned long (*op)(unsigned long),
             unsigned long arg)
      {
        unsigned long v;
        __asm__ volatile ("cli");
        v = (*op)(arg);
        __asm__ volatile ("sti");
        return v;
      }
    
    Then it pagefaults in that "atomic" section, triggering the warning.
    
    There is no way the kernel could provide "atomicity" in this path,
    a page fault is a cannot-continue machine event so the kernel has to
    wait for the page to be filled in.
    
    Even if it was just a minor fault we'd have to take locks and might have
    to spend quite a bit of time with interrupts disabled - not nice to irq
    latencies in general.
    
    So instead just enable interrupts in the pagefault path unconditionally
    if we come from user-space, and handle the fault.
    
    Also, while touching this code, unify some trivial parts of the x86
    VM paths at the same time.
    
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    Reported-by: Arjan van de Ven <arjan at infradead.org>
    Signed-off-by: Ingo Molnar <mingo at elte.hu>

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index a742d75..ac2ad78 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -645,24 +645,23 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 	}
 
 
-#ifdef CONFIG_X86_32
-	/* It's safe to allow irq's after cr2 has been saved and the vmalloc
-	   fault has been handled. */
-	if (regs->flags & (X86_EFLAGS_IF | X86_VM_MASK))
-		local_irq_enable();
-
 	/*
-	 * If we're in an interrupt, have no user context or are running in an
-	 * atomic region then we must not take the fault.
+	 * It's safe to allow irq's after cr2 has been saved and the
+	 * vmalloc fault has been handled.
+	 *
+	 * User-mode registers count as a user access even for any
+	 * potential system fault or CPU buglet.
 	 */
-	if (in_atomic() || !mm)
-		goto bad_area_nosemaphore;
-#else /* CONFIG_X86_64 */
-	if (likely(regs->flags & X86_EFLAGS_IF))
+	if (user_mode_vm(regs)) {
+		local_irq_enable();
+		error_code |= PF_USER;
+	} else if (regs->flags & X86_EFLAGS_IF)
 		local_irq_enable();
 
+#ifdef CONFIG_X86_64
 	if (unlikely(error_code & PF_RSVD))
 		pgtable_bad(address, regs, error_code);
+#endif
 
 	/*
 	 * If we're in an interrupt, have no user context or are running in an
@@ -671,14 +670,7 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 	if (unlikely(in_atomic() || !mm))
 		goto bad_area_nosemaphore;
 
-	/*
-	 * User-mode registers count as a user access even for any
-	 * potential system fault or CPU buglet.
-	 */
-	if (user_mode_vm(regs))
-		error_code |= PF_USER;
 again:
-#endif
 	/* 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.  Unfortunately, in the case of an


Index: kernel.spec
===================================================================
RCS file: /cvs/pkgs/rpms/kernel/devel/kernel.spec,v
retrieving revision 1.1117
retrieving revision 1.1118
diff -u -r1.1117 -r1.1118
--- kernel.spec	5 Nov 2008 21:15:52 -0000	1.1117
+++ kernel.spec	5 Nov 2008 21:45:12 -0000	1.1118
@@ -610,6 +610,7 @@
 Patch270: linux-2.6-debug-taint-vm.patch
 Patch280: linux-2.6-debug-spinlock-taint.patch
 Patch340: linux-2.6-debug-vm-would-have-oomkilled.patch
+Patch341: linux-2.6-mm-pagefault-enable-ints.patch
 Patch360: linux-2.6-debug-always-inline-kzalloc.patch
 Patch370: linux-2.6-crash-driver.patch
 Patch380: linux-2.6-defaults-pci_no_msi.patch
@@ -1186,6 +1187,7 @@
 ApplyPatch linux-2.6-debug-taint-vm.patch
 ApplyPatch linux-2.6-debug-spinlock-taint.patch
 ApplyPatch linux-2.6-debug-vm-would-have-oomkilled.patch
+ApplyPatch linux-2.6-mm-pagefault-enable-ints.patch
 ApplyPatch linux-2.6-debug-always-inline-kzalloc.patch
 
 #
@@ -1922,6 +1924,9 @@
 %kernel_variant_files -k vmlinux %{with_kdump} kdump
 
 %changelog
+* Wed Nov 05 2008 Dave Jones <davej at redhat.com> 2.6.27.4-82
+- x86/mm: do not trigger a kernel warning if user-space disables interrupts and generates a page fault
+
 * Wed Nov 05 2008 Dave Jones <davej at redhat.com> 2.6.27.4-81
 - ACPI: Ignore AE_NOT_FOUND error of EC _REG method and continue to initialize EC (#435653)