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uml: fix irqstack crash

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This patch fixes a crash caused by an interrupt coming in when an IRQ stack
is being torn down.  When this happens, handle_signal will loop, setting up
the IRQ stack again because the tearing down had finished, and handling
whatever signals had come in.

However, to_irq_stack returns a mask of pending signals to be handled, plus
bit zero is set if the IRQ stack was already active, and thus shouldn't be
torn down.  This causes a problem because when handle_signal goes around
the loop, sig will be zero, and to_irq_stack will duly set bit zero in the
returned mask, faking handle_signal into believing that it shouldn't tear
down the IRQ stack and return thread_info pointers back to their original
values.

This will eventually cause a crash, as the IRQ stack thread_info will
continue pointing to the original task_struct and an interrupt will look
into it after it has been freed.

The fix is to stop passing a signal number into to_irq_stack.  Rather, the
pending signals mask is initialized beforehand with the bit for sig already
set.  References to sig in to_irq_stack can be replaced with references to
the mask.

[akpm@linux-foundation.org: use UL]
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jeff Dike
2007-09-18 22:46:49 -07:00
committed by Linus Torvalds
parent 480eccf9ae
commit 508a92741a
3 changed files with 7 additions and 6 deletions
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7
arch/um/kernel/irq.c
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@@ -518,13 +518,13 @@ int init_aio_irq(int irq, char *name, irq_handler_t handler)
static unsigned long pending_mask;
unsigned long to_irq_stack(int sig, unsigned long *mask_out)
unsigned long to_irq_stack(unsigned long *mask_out)
{
struct thread_info *ti;
unsigned long mask, old;
int nested;
mask = xchg(&pending_mask, 1 << sig);
mask = xchg(&pending_mask, *mask_out);
if(mask != 0){
/* If any interrupts come in at this point, we want to
* make sure that their bits aren't lost by our
@@ -534,7 +534,7 @@ unsigned long to_irq_stack(int sig, unsigned long *mask_out)
* and pending_mask contains a bit for each interrupt
* that came in.
*/
old = 1 << sig;
old = *mask_out;
do {
old |= mask;
mask = xchg(&pending_mask, old);
@@ -550,6 +550,7 @@ unsigned long to_irq_stack(int sig, unsigned long *mask_out)
task = cpu_tasks[ti->cpu].task;
tti = task_thread_info(task);
*ti = *tti;
ti->real_thread = tti;
task->stack = ti;