Patch "parisc: fix interruption handler to respect pagefault_disable()" has been added to the 3.10-stable tree

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This is a note to let you know that I've just added the patch titled

    parisc: fix interruption handler to respect pagefault_disable()

to the 3.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     parisc-fix-interruption-handler-to-respect-pagefault_disable.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 59b33f148cc08fb33cbe823fca1e34f7f023765e Mon Sep 17 00:00:00 2001
From: Helge Deller <deller@xxxxxx>
Date: Tue, 1 Oct 2013 21:54:46 +0200
Subject: parisc: fix interruption handler to respect pagefault_disable()

From: Helge Deller <deller@xxxxxx>

commit 59b33f148cc08fb33cbe823fca1e34f7f023765e upstream.

Running an "echo t > /proc/sysrq-trigger" crashes the parisc kernel.  The
problem is, that in print_worker_info() we try to read the workqueue info via
the probe_kernel_read() functions which use pagefault_disable() to avoid
crashes like this:
    probe_kernel_read(&pwq, &worker->current_pwq, sizeof(pwq));
    probe_kernel_read(&wq, &pwq->wq, sizeof(wq));
    probe_kernel_read(name, wq->name, sizeof(name) - 1);

The problem here is, that the first probe_kernel_read(&pwq) might return zero
in pwq and as such the following probe_kernel_reads() try to access contents of
the page zero which is read protected and generate a kernel segfault.

With this patch we fix the interruption handler to call parisc_terminate()
directly only if pagefault_disable() was not called (in which case
preempt_count()==0).  Otherwise we hand over to the pagefault handler which
will try to look up the faulting address in the fixup tables.

Signed-off-by: Helge Deller <deller@xxxxxx>
Signed-off-by: John David Anglin  <dave.anglin@xxxxxxxx>
Signed-off-by: Helge Deller <deller@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/parisc/kernel/traps.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/parisc/kernel/traps.c
+++ b/arch/parisc/kernel/traps.c
@@ -805,14 +805,14 @@ void notrace handle_interruption(int cod
 	else {
 
 	    /*
-	     * The kernel should never fault on its own address space.
+	     * The kernel should never fault on its own address space,
+	     * unless pagefault_disable() was called before.
 	     */
 
-	    if (fault_space == 0) 
+	    if (fault_space == 0 && !in_atomic())
 	    {
 		pdc_chassis_send_status(PDC_CHASSIS_DIRECT_PANIC);
 		parisc_terminate("Kernel Fault", regs, code, fault_address);
-	
 	    }
 	}
 


Patches currently in stable-queue which might be from deller@xxxxxx are

queue-3.10/parisc-fix-interruption-handler-to-respect-pagefault_disable.patch
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