Re: Traceback with CONFIG_REGMAP_KUNIT=y+CONFIG_DEBUG_ATOMIC_SLEEP=y

[Guenter Roeck]

On 7/20/23 09:25, Guenter Roeck wrote:
> On 7/20/23 08:07, Mark Brown wrote:
> > On Thu, Jul 20, 2023 at 08:03:13AM -0700, Guenter Roeck wrote:
> > > On 7/20/23 07:31, Mark Brown wrote:
> >
> > > > They're both independently fine, but I wouldn't expect anything that's
> > > > running in atomic context to be actually using dynamic allocations.
> >
> > > Which one do you prefer ? As I mentioned in my second patch, there are
> > > two drivers which use fast_io together with REGCACHE_RBTREE and thus
> > > are likely affected by this problem. Dan's solution would cover that,
> > > while my current RFC patch would likely cause those drivers to fail.
> > > Plus, of course, they could get stuck if they actually end up trying to
> > > sleep while allocating memory.
> >
> > Like I say I don't think it's an either/or - we can do both
> > independently, they both make sense standalone and don't conflict with
> > each other.
>
> I guess I am missing something. I have not tried it, but wouldn't my patches
> be unnecessary if Dan's patch is applied ?

Actually, Dan's patch isn't complete. With it applied:

[    4.816104]     # Subtest: regmap
[    4.816175]     1..22
[    4.816266]         KTAP version 1
[    4.816343]         # Subtest: basic_read_write
[    4.821773]         ok 1 none
[    4.827032]         ok 2 flat
[    4.832404]         ok 3 rbtree
[    4.834664] BUG: sleeping function called from invalid context at include/linux/sched/mm.h:306
[    4.834935] in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 167, name: kunit_try_catch
[    4.835059] preempt_count: 1, expected: 0
[    4.835198] 1 lock held by kunit_try_catch/167:
[    4.835297]  #0: 838e9c10 (regmap_kunit:86:(config)->lock){....}-{2:2}, at: regmap_lock_spinlock+0x14/0x1c
[    4.835980] irq event stamp: 146
[    4.836057] hardirqs last  enabled at (145): [<8078bfa8>] crng_make_state+0x1a0/0x294
[    4.836176] hardirqs last disabled at (146): [<80c5f62c>] _raw_spin_lock_irqsave+0x7c/0x80
[    4.836297] softirqs last  enabled at (0): [<80110cc4>] copy_process+0x810/0x216c
[    4.836413] softirqs last disabled at (0): [<00000000>] 0x0
[    4.836628] CPU: 0 PID: 167 Comm: kunit_try_catch Tainted: G                 N 6.5.0-rc1-00028-gc4be22597a36-dirty #6
[    4.836809] Hardware name: Generic DT based system
[    4.837002]  unwind_backtrace from show_stack+0x18/0x1c
[    4.837134]  show_stack from dump_stack_lvl+0x38/0x5c
[    4.837229]  dump_stack_lvl from __might_resched+0x188/0x2d0
[    4.837325]  __might_resched from __kmem_cache_alloc_node+0x1f4/0x258
[    4.837426]  __kmem_cache_alloc_node from __kmalloc+0x48/0x170
[    4.837521]  __kmalloc from regcache_maple_write+0x194/0x248
[    4.837617]  regcache_maple_write from _regmap_write+0x88/0x140
[    4.837711]  _regmap_write from regmap_write+0x44/0x68
[    4.837797]  regmap_write from basic_read_write+0x8c/0x27c
[    4.837889]  basic_read_write from kunit_generic_run_threadfn_adapter+0x1c/0x28
[    4.837996]  kunit_generic_run_threadfn_adapter from kthread+0xf8/0x120
[    4.838099]  kthread from ret_from_fork+0x14/0x3c
[    4.838214] Exception stack(0x881a5fb0 to 0x881a5ff8)
[    4.838346] 5fa0:                                     00000000 00000000 00000000 00000000
[    4.838465] 5fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    4.838576] 5fe0: 00000000 00000000 00000000 00000000 00000013 00000000
[    4.841868]         ok 4 maple
[    4.841923]     # basic_read_write: pass:4 fail:0 skip:0 total:4
[    4.842022]     ok 1 basic_read_write

It would have to be extended to also address the same problem in the maple tree
code. Also, the change would probably not be needed in regcache_rbtree_init().

After adding the GFP_KERNEL -> map->alloc_flags changes to the maple tree
code while skipping the init functions, I no longer see the traceback.
This is without my patches.

Thanks,
Guenter