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

Commit Message

Andrew Morton Nov. 5, 2021, 8:35 p.m. UTC

From: Marco Elver <[e-mail]>
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/[e-mail]


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/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Marco Elver <[e-mail]>
Tested-by: Shuah Khan <[e-mail]>
Acked-by: Sebastian Andrzej Siewior <[e-mail]>
Reviewed-by: Andrey Konovalov <[e-mail]>
Cc: Tejun Heo <[e-mail]>
Cc: Lai Jiangshan <[e-mail]>
Cc: Walter Wu <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Cc: Alexander Potapenko <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Vijayanand Jitta <[e-mail]>
Cc: Vinayak Menon <[e-mail]>
Cc: "Gustavo A. R. Silva" <[e-mail]>
Cc: Taras Madan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

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

Patch

--- 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,