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Date:   Sat, 23 Oct 2021 08:59:32 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Jessica Zhang <jesszhan@...eaurora.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Maxime Ripard <maxime@...no.tech>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Krishna Manikandan <mkrishn@...eaurora.org>,
        Kalyan Thota <kalyan_t@...eaurora.org>,
        Mark Yacoub <markyacoub@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] drm/msm/dpu: Remove dynamic allocation from atomic context

On Fri, Oct 22, 2021 at 12:15 PM Jessica Zhang <jesszhan@...eaurora.org> wrote:
>
> On 10/22/2021 10:20 AM, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.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@...omium.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 = ...`
>

I was trying to avoid moving that because I've seen tools flag things
like that as use-before-init before.  But I guess I can use
BUILD_BUG_ON() instead.

BR,
-R

> 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,

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