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 commit
ab00db21).

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.comSigned-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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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,