parisc: fix interruption handler to respect pagefault_disable()

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@gmx.de>
Cc: <stable@vger.kernel.org> # v3.0+
Signed-off-by: John David Anglin  <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c
index ebc877c28583ac38d33a9dc04e08f6d69df0d180..1cd1d0c83b6d7bd7a21d0a22c57e18f2ac27f65a 100644 (file)
--- a/arch/parisc/kernel/traps.c
+++ b/arch/parisc/kernel/traps.c
@@ -800,14 +800,14 @@ void notrace handle_interruption(int code, struct pt_regs *regs)
        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);
-       
            }
        }