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 <cmetc...@tilera.com>
---
arch/tile/include/asm/processor.h | 2 ++
arch/tile/kernel/stack.c | 30 ++++++++++++++++++++++++++++--
2 files changed, 30 insertions(+), 2 deletions(-)
diff --git a/arch/tile/include/asm/processor.h
b/arch/tile/include/asm/processor.h
index cda2724..fed1c04 100644
--- a/arch/tile/include/asm/processor.h
+++ b/arch/tile/include/asm/processor.h
@@ -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;
diff --git a/arch/tile/kernel/stack.c b/arch/tile/kernel/stack.c
index af8dfc9..c972689 100644
--- a/arch/tile/kernel/stack.c
+++ b/arch/tile/kernel/stack.c
@@ -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) {
@@ -352,6 +351,26 @@ static void describe_addr(struct KBacktraceIterator *kbt,
}
/*
+ * 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()
* and dump_stack() (in entry.S) are architecture-independent entry points.
@@ -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);
--
1.8.3.1
--
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