Re: [PATCH] drm: fb-helper: Avoid nesting spinlock_t into raw_spinlock_t

From: Sebastian Siewior
Date: Tue Feb 15 2022 - 10:49:17 EST

On 2022-02-15 16:43:08 [+0100], Jiri Kosina wrote:
> From: Jiri Kosina <jkosina@xxxxxxx>
>
> drm_fb_helper_damage() is acquiring spinlock_t (helper->damage_lock),
> while it can be called from contexts where raw_spinlock_t is held (e.g.
> console_owner lock obtained on vprintk_emit() codepath).
>
> As the critical sections protected by damage_lock are super-tiny, let's
> fix this by converting it to raw_spinlock_t in order not to violate
> PREEMPT_RT-imposed lock nesting rules.
>
> This fixes the splat below.
>
> =============================
> [ BUG: Invalid wait context ]
> 5.17.0-rc4-00002-gd567f5db412e #1 Not tainted

rc4. Is this also the case in the RT tree which includes John's printk
changes?

> -----------------------------
> swapper/0/0 is trying to lock:
> ffff8c5687cc4158 (&helper->damage_lock){....}-{3:3}, at: drm_fb_helper_damage.isra.22+0x4a/0xf0
> other info that might help us debug this:
> context-{2:2}
> 3 locks held by swapper/0/0:
> #0: ffffffffad776520 (console_lock){+.+.}-{0:0}, at: vprintk_emit+0xb8/0x2a0
> #1: ffffffffad696120 (console_owner){-...}-{0:0}, at: console_unlock+0x17f/0x550
> #2: ffffffffad926a58 (printing_lock){....}-{3:3}, at: vt_console_print+0x7d/0x3e0
> stack backtrace:
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.17.0-rc4-00002-gd567f5db412e #1 bed1d5e19e0e7e8c9d97fd8afa1322f7f47a4f38
> Hardware name: LENOVO 20UJS2B905/20UJS2B905, BIOS R1CET63W(1.32 ) 04/09/2021
> Call Trace:
> <IRQ>
> dump_stack_lvl+0x58/0x71
> __lock_acquire+0x165b/0x1780
> ? secondary_startup_64_no_verify+0xd5/0xdb
> lock_acquire+0x278/0x300
> ? drm_fb_helper_damage.isra.22+0x4a/0xf0
> ? save_trace+0x3e/0x340
> ? __bfs+0x10f/0x240
> _raw_spin_lock_irqsave+0x48/0x60
> ? drm_fb_helper_damage.isra.22+0x4a/0xf0
> drm_fb_helper_damage.isra.22+0x4a/0xf0
> soft_cursor+0x194/0x240
> bit_cursor+0x386/0x630
> ? get_color+0x29/0x120
> ? bit_putcs+0x4b0/0x4b0
> ? console_unlock+0x17f/0x550
> hide_cursor+0x2f/0x90
> vt_console_print+0x3c5/0x3e0
> ? console_unlock+0x17f/0x550
> console_unlock+0x515/0x550
> vprintk_emit+0x1c8/0x2a0
> _printk+0x52/0x6e
> ? sched_clock_tick+0x3d/0x60
> collect_cpu_info_amd+0x93/0xd0
> collect_cpu_info_local+0x23/0x30
> flush_smp_call_function_queue+0x137/0x220
> __sysvec_call_function_single+0x43/0x1c0
> sysvec_call_function_single+0x43/0x80
> </IRQ>
> <TASK>
> asm_sysvec_call_function_single+0x12/0x20
> RIP: 0010:cpuidle_enter_state+0x111/0x4b0
> Code: 7c ff 45 84 ff 74 17 9c 58 0f 1f 44 00 00 f6 c4 02 0f 85 71 03 00 00 31 ff e8 bb 21 86 ff e8 76 2f 8e ff fb 66 0f 1f 44 00 00 <45> 85 f6 0f 88 12 01 00 00 49 63 d6 4c 2b 24 24 48 8d 04 52 48 8d
> RSP: 0018:ffffffffad603e48 EFLAGS: 00000206
> RAX: 00000000000127c3 RBX: 0000000000000003 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffac32617a
> RBP: ffff8c5687ba4400 R08: 0000000000000001 R09: 0000000000000001
> R10: ffffffffad603e10 R11: 0000000000000000 R12: 00000000685eb4a0
> R13: ffffffffad918f80 R14: 0000000000000003 R15: 0000000000000000
> ? cpuidle_enter_state+0x10a/0x4b0
> ? cpuidle_enter_state+0x10a/0x4b0
> cpuidle_enter+0x29/0x40
> do_idle+0x24d/0x2c0
> cpu_startup_entry+0x19/0x20
> start_kernel+0x9c2/0x9e9
> secondary_startup_64_no_verify+0xd5/0xdb
> </TASK>
>
> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
> ---
> drivers/gpu/drm/drm_fb_helper.c | 14 +++++++-------
> include/drm/drm_fb_helper.h | 2 +-
> 2 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index ed43b987d306..7c4ab6e6f865 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -436,11 +436,11 @@ static void drm_fb_helper_damage_work(struct work_struct *work)
> unsigned long flags;
> int ret;
>
> - spin_lock_irqsave(&helper->damage_lock, flags);
> + raw_spin_lock_irqsave(&helper->damage_lock, flags);
> clip_copy = *clip;
> clip->x1 = clip->y1 = ~0;
> clip->x2 = clip->y2 = 0;
> - spin_unlock_irqrestore(&helper->damage_lock, flags);
> + raw_spin_unlock_irqrestore(&helper->damage_lock, flags);
>
> /* Call damage handlers only if necessary */
> if (!(clip_copy.x1 < clip_copy.x2 && clip_copy.y1 < clip_copy.y2))
> @@ -465,12 +465,12 @@ static void drm_fb_helper_damage_work(struct work_struct *work)
> * Restore damage clip rectangle on errors. The next run
> * of the damage worker will perform the update.
> */
> - spin_lock_irqsave(&helper->damage_lock, flags);
> + raw_spin_lock_irqsave(&helper->damage_lock, flags);
> clip->x1 = min_t(u32, clip->x1, clip_copy.x1);
> clip->y1 = min_t(u32, clip->y1, clip_copy.y1);
> clip->x2 = max_t(u32, clip->x2, clip_copy.x2);
> clip->y2 = max_t(u32, clip->y2, clip_copy.y2);
> - spin_unlock_irqrestore(&helper->damage_lock, flags);
> + raw_spin_unlock_irqrestore(&helper->damage_lock, flags);
> }
>
> /**
> @@ -486,7 +486,7 @@ void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
> const struct drm_fb_helper_funcs *funcs)
> {
> INIT_LIST_HEAD(&helper->kernel_fb_list);
> - spin_lock_init(&helper->damage_lock);
> + raw_spin_lock_init(&helper->damage_lock);
> INIT_WORK(&helper->resume_work, drm_fb_helper_resume_worker);
> INIT_WORK(&helper->damage_work, drm_fb_helper_damage_work);
> helper->damage_clip.x1 = helper->damage_clip.y1 = ~0;
> @@ -670,12 +670,12 @@ static void drm_fb_helper_damage(struct fb_info *info, u32 x, u32 y,
> if (!drm_fbdev_use_shadow_fb(helper))
> return;
>
> - spin_lock_irqsave(&helper->damage_lock, flags);
> + raw_spin_lock_irqsave(&helper->damage_lock, flags);
> clip->x1 = min_t(u32, clip->x1, x);
> clip->y1 = min_t(u32, clip->y1, y);
> clip->x2 = max_t(u32, clip->x2, x + width);
> clip->y2 = max_t(u32, clip->y2, y + height);
> - spin_unlock_irqrestore(&helper->damage_lock, flags);
> + raw_spin_unlock_irqrestore(&helper->damage_lock, flags);
>
> schedule_work(&helper->damage_work);
> }
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index 3af4624368d8..91178958896e 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -131,7 +131,7 @@ struct drm_fb_helper {
> struct fb_info *fbdev;
> u32 pseudo_palette[17];
> struct drm_clip_rect damage_clip;
> - spinlock_t damage_lock;
> + raw_spinlock_t damage_lock;
> struct work_struct damage_work;
> struct work_struct resume_work;
>
>

Sebastian