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Commit 3ef23111 authored by Chris Metcalf's avatar Chris Metcalf
Browse files

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: default avatarChris Metcalf <cmetcalf@tilera.com>
parent 2f9ac29e

arch/tile/include/asm/processor.h

+2 −0
Original line number Diff line number Diff line
@@ -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;

arch/tile/kernel/stack.c

+28 −2
Original line number Diff line number Diff line
@@ -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);