parisc: fix interruption handler to respect pagefault_disable()
authorHelge Deller <deller@gmx.de>
Tue, 1 Oct 2013 19:54:46 +0000 (21:54 +0200)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Tue, 22 Oct 2013 07:41:44 +0000 (08:41 +0100)
commitac008905d50badfe8b695fa3f1eef20ac352e3e6
treebb51be0f6e7992abf9eea1c67f0789c4fcef52be
parent546a50594e6241e2002cddbef7c350e177e08e52
parisc: fix interruption handler to respect pagefault_disable()

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@gmx.de>
Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
arch/parisc/kernel/traps.c