Re: [PATCH 2/2] drm/msm/dpu: Remove dynamic allocation from atomic context

[Jessica Zhang <jesszhan@codeaurora.org>]

On 10/22/2021 10:20 AM, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
>
> We know the upper bound on # of mixers (ie. two), so lets just allocate
> this on the stack.
>
> Fixes:
>
>     BUG: sleeping function called from invalid context at include/linux/sched/mm.h:201
>     in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/0
>     INFO: lockdep is turned off.
>     irq event stamp: 43642
>     hardirqs last  enabled at (43641): [<ffffffe24dd276bc>] cpuidle_enter_state+0x158/0x25c
>     hardirqs last disabled at (43642): [<ffffffe24dfff450>] enter_el1_irq_or_nmi+0x10/0x1c
>     softirqs last  enabled at (43620): [<ffffffe24d4103fc>] __do_softirq+0x1e4/0x464
>     softirqs last disabled at (43615): [<ffffffe24d48bd90>] __irq_exit_rcu+0x104/0x150
>     CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W         5.15.0-rc3-debug+ #105
>     Hardware name: Google Lazor (rev1 - 2) with LTE (DT)
>     Call trace:
>      dump_backtrace+0x0/0x18c
>      show_stack+0x24/0x30
>      dump_stack_lvl+0xa0/0xd4
>      dump_stack+0x18/0x34
>      ___might_sleep+0x1e0/0x1f0
>      __might_sleep+0x78/0x8c
>      slab_pre_alloc_hook.constprop.0+0x48/0x6c
>      __kmalloc+0xc8/0x21c
>      dpu_crtc_vblank_callback+0x158/0x1f8
>      dpu_encoder_vblank_callback+0x70/0xc4
>      dpu_encoder_phys_vid_vblank_irq+0x50/0x12c
>      dpu_core_irq+0x1bc/0x1d0
>      dpu_irq+0x1c/0x28
>      msm_irq+0x34/0x40
>      __handle_irq_event_percpu+0x15c/0x308
>      handle_irq_event_percpu+0x3c/0x90
>      handle_irq_event+0x54/0x98
>      handle_level_irq+0xa0/0xd0
>      handle_irq_desc+0x2c/0x44
>      generic_handle_domain_irq+0x28/0x34
>      dpu_mdss_irq+0x90/0xe8
>      handle_irq_desc+0x2c/0x44
>      handle_domain_irq+0x54/0x80
>      gic_handle_irq+0xd4/0x148
>      call_on_irq_stack+0x2c/0x54
>      do_interrupt_handler+0x4c/0x64
>      el1_interrupt+0x30/0xd0
>      el1h_64_irq_handler+0x18/0x24
>      el1h_64_irq+0x78/0x7c
>      arch_local_irq_enable+0xc/0x14
>      cpuidle_enter+0x44/0x5c
>      do_idle+0x248/0x268
>      cpu_startup_entry+0x30/0x48
>      rest_init+0x188/0x19c
>      arch_call_rest_init+0x1c/0x28
>      start_kernel+0x704/0x744
>      __primary_switched+0xc0/0xc8
>
> Fixes: 78d9b458cc21 ("drm/msm/dpu: Add CRC support for DPU")
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 16 +++++-----------
>   1 file changed, 5 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> index 0ae397044310..80c0ae688734 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> @@ -182,21 +182,19 @@ static int dpu_crtc_get_crc(struct drm_crtc *crtc)
>   {
>   	struct dpu_crtc_state *crtc_state;
>   	struct dpu_crtc_mixer *m;
> -	u32 *crcs;
> +	u32 crcs[CRTC_DUAL_MIXERS];
>   
>   	int i = 0;
>   	int rc = 0;
>   
>   	crtc_state = to_dpu_crtc_state(crtc->state);
> -	crcs = kcalloc(crtc_state->num_mixers, sizeof(*crcs), GFP_KERNEL);
>   
> -	if (!crcs)
> -		return -ENOMEM;
> +	static_assert(ARRAY_SIZE(crcs) == ARRAY_SIZE(crtc_state->mixers));
>   

Getting a C90 compiler warning for static_assert():

     In file included from ./include/linux/bits.h:22,
                     from ./include/linux/bitops.h:6,
                     from ./include/linux/kernel.h:12,
                     from ./include/linux/list.h:9,
                     from ./include/linux/wait.h:7,
                     from ./include/linux/wait_bit.h:8,
                     from ./include/linux/fs.h:6,
                     from ./include/linux/debugfs.h:15,
                     from drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c:10:
     drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c: In function 
‘dpu_crtc_get_crc’:
     ./include/linux/build_bug.h:78:41: warning: ISO C90 forbids mixed 
declarations and code [-Wdeclaration-after-statement]
         78 | #define __static_assert(expr, msg, ...) 
_Static_assert(expr, msg)
         |                                         ^~~~~~~~~~~~~~
     ./include/linux/build_bug.h:77:34: note: in expansion of macro 
‘__static_assert’
         77 | #define static_assert(expr, ...) __static_assert(expr, 
##__VA_ARGS__, #expr)
         |                                  ^~~~~~~~~~~~~~~
     drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c:192:2: note: in expansion 
of macro ‘static_assert’
     192 |  static_assert(ARRAY_SIZE(crcs) == 
ARRAY_SIZE(crtc_state->mixers));
         |  ^~~~~~~~~~~~~

Can be fixed by moving the static_assert() before `crtc_state = ...`

Thanks,

Jessica Zhang

>   	/* Skip first 2 frames in case of "uncooked" CRCs */
>   	if (crtc_state->crc_frame_skip_count < 2) {
>   		crtc_state->crc_frame_skip_count++;
> -		goto cleanup;
> +		return 0;
>   	}
>   
>   	for (i = 0; i < crtc_state->num_mixers; ++i) {
> @@ -210,16 +208,12 @@ static int dpu_crtc_get_crc(struct drm_crtc *crtc)
>   
>   		if (rc) {
>   			DRM_DEBUG_DRIVER("MISR read failed\n");
> -			goto cleanup;
> +			return rc;
>   		}
>   	}
>   
> -	rc = drm_crtc_add_crc_entry(crtc, true,
> +	return drm_crtc_add_crc_entry(crtc, true,
>   			drm_crtc_accurate_vblank_count(crtc), crcs);
> -
> -cleanup:
> -	kfree(crcs);
> -	return rc;
>   }
>   
>   static bool dpu_crtc_get_scanout_position(struct drm_crtc *crtc,