On 2022-02-15 16:43:08 [+0100], Jiri Kosina wrote:

From: Jiri Kosina jkosina@suse.cz

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@suse.cz

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