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tile: avoid recursive backtrace faults 

This change adds support for avoiding recursive backtracer crashes;
we haven't seen this in practice other than when things are seriously
corrupt, but it may help avoid losing the root cause of a crash.

Also, don't abort kernel backtracers for invalid userspace PC's.
If we do, we lose the ability to backtrace through a userspace
call to a bad address above PAGE_OFFSET, even though that it can
be perfectly reasonable to continue the backtrace in such a case.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
This commit is contained in:
Chris Metcalf 2013-08-06 16:10:23 -04:00
parent 2f9ac29eec
commit 3ef2311154
2 changed files with 30 additions and 2 deletions
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2
arch/tile/include/asm/processor.h
View File

@ -110,6 +110,8 @@ struct thread_struct {
unsigned long long interrupt_mask;
/* User interrupt-control 0 state */
unsigned long intctrl_0;
/* Is this task currently doing a backtrace? */
bool in_backtrace;
#if CHIP_HAS_PROC_STATUS_SPR()
/* Any other miscellaneous processor state bits */
unsigned long proc_status;

30
arch/tile/kernel/stack.c
View File

@ -103,8 +103,7 @@ static struct pt_regs *valid_fault_handler(struct KBacktraceIterator* kbt)
if (kbt->verbose)
pr_err(" <%s while in kernel mode>\n", fault);
} else if (EX1_PL(p->ex1) == USER_PL &&
p->pc < PAGE_OFFSET &&
p->sp < PAGE_OFFSET) {
p->sp < PAGE_OFFSET && p->sp != 0) {
if (kbt->verbose)
pr_err(" <%s while in user mode>\n", fault);
} else if (kbt->verbose) {
@ -351,6 +350,26 @@ static void describe_addr(struct KBacktraceIterator *kbt,
vma->vm_start, vma->vm_end - vma->vm_start);
}
/*
* Avoid possible crash recursion during backtrace. If it happens, it
* makes it easy to lose the actual root cause of the failure, so we
* put a simple guard on all the backtrace loops.
*/
static bool start_backtrace(void)
{
if (current->thread.in_backtrace) {
pr_err("Backtrace requested while in backtrace!\n");
return false;
}
current->thread.in_backtrace = true;
return true;
}
static void end_backtrace(void)
{
current->thread.in_backtrace = false;
}
/*
* This method wraps the backtracer's more generic support.
* It is only invoked from the architecture-specific code; show_stack()
@ -361,6 +380,8 @@ void tile_show_stack(struct KBacktraceIterator *kbt, int headers)
int i;
int have_mmap_sem = 0;
if (!start_backtrace())
return;
if (headers) {
/*
* Add a blank line since if we are called from panic(),
@ -402,6 +423,7 @@ void tile_show_stack(struct KBacktraceIterator *kbt, int headers)
pr_err("Stack dump complete\n");
if (have_mmap_sem)
up_read(&kbt->task->mm->mmap_sem);
end_backtrace();
}
EXPORT_SYMBOL(tile_show_stack);
@ -463,6 +485,8 @@ void save_stack_trace_tsk(struct task_struct *task, struct stack_trace *trace)
int skip = trace->skip;
int i = 0;
if (!start_backtrace())
goto done;
if (task == NULL || task == current)
KBacktraceIterator_init_current(&kbt);
else
@ -476,6 +500,8 @@ void save_stack_trace_tsk(struct task_struct *task, struct stack_trace *trace)
break;
trace->entries[i++] = kbt.it.pc;
}
end_backtrace();
done:
trace->nr_entries = i;
}
EXPORT_SYMBOL(save_stack_trace_tsk);