[patch 019/262] lib/stackdepot: include gfp.h

Andrew Morton
2021-11-05T20:35:38Z

From: Marco Elver <elver@google.com>
Subject: lib/stackdepot: include gfp.h

Patch series "stackdepot, kasan, workqueue: Avoid expanding stackdepot slabs when holding raw_spin_lock", v2.

Shuah Khan reported [1]:

| When CONFIG_PROVE_RAW_LOCK_NESTING=y and CONFIG_KASAN are enabled,
| kasan_record_aux_stack() runs into "BUG: Invalid wait context" when
| it tries to allocate memory attempting to acquire spinlock in page
| allocation code while holding workqueue pool raw_spinlock.
|
| There are several instances of this problem when block layer tries
| to __queue_work(). Call trace from one of these instances is below:
|
| kblockd_mod_delayed_work_on()
| mod_delayed_work_on()
| __queue_delayed_work()
| __queue_work() (rcu_read_lock, raw_spin_lock pool->lock held)
| insert_work()
| kasan_record_aux_stack()
| kasan_save_stack()
| stack_depot_save()
| alloc_pages()
| __alloc_pages()
| get_page_from_freelist()
| rm_queue()
| rm_queue_pcplist()
| local_lock_irqsave(&pagesets.lock, flags);
| [ BUG: Invalid wait context triggered ]

PROVE_RAW_LOCK_NESTING is pointing out that (on RT kernels) the locking
rules are being violated. More generally, memory is being allocated from
a non-preemptive context (raw_spin_lock'd c-s) where it is not allowed.

To properly fix this, we must prevent stackdepot from replenishing its
"stack slab" pool if memory allocations cannot be done in the current
context: it's a bug to use either GFP_ATOMIC nor GFP_NOWAIT in certain
non-preemptive contexts, including raw_spin_locks (see gfp.h and
ab00db216c9c7).

The only downside is that saving a stack trace may fail if: stackdepot
runs out of space AND the same stack trace has not been recorded before.
I expect this to be unlikely, and a simple experiment (boot the kernel)
didn't result in any failure to record stack trace from insert_work().

The series includes a few minor fixes to stackdepot that I noticed in
preparing the series. It then introduces __stack_depot_save(), which
exposes the option to force stackdepot to not allocate any memory.
Finally, KASAN is changed to use the new stackdepot interface and provide
kasan_record_aux_stack_noalloc(), which is then used by workqueue code.

[1] https://lkml.kernel.org/r/20210902200134.25603-1-skhan@linuxfoundation.org

This patch (of 6):

<linux/stackdepot.h> refers to gfp_t, but doesn't include gfp.h.

Fix it by including <linux/gfp.h>.

Link: https://lkml.kernel.org/r/20210913112609.2651084-1-elver@google.com
Link: https://lkml.kernel.org/r/20210913112609.2651084-2-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Tested-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Walter Wu <walter-zh.wu@mediatek.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Cc: Vinayak Menon <vinmenon@codeaurora.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Taras Madan <tarasmadan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/stackdepot.h | 2 ++
1 file changed, 2 insertions(+)

--- a/include/linux/stackdepot.h~lib-stackdepot-include-gfph
+++ a/include/linux/stackdepot.h
@@ -11,6 +11,8 @@
#ifndef _LINUX_STACKDEPOT_H
#define _LINUX_STACKDEPOT_H

+#include <linux/gfp.h>
+
typedef u32 depot_stack_handle_t;

depot_stack_handle_t stack_depot_save(unsigned long *entries,
_