From 217ac2ce39c639792d10169a7c3bfb970b9e1869 Mon Sep 17 00:00:00 2001 From: Tvrtko Ursulin Date: Tue, 13 Aug 2024 11:25:05 +0100 Subject: [PATCH] drm/v3d: Appease lockdep while updating GPU stats MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Lockdep thinks our seqcount_t usage is unsafe because the update path can be both from irq and worker context: [ ] ================================ [ ] WARNING: inconsistent lock state [ ] 6.10.3-v8-16k-numa #159 Tainted: G WC [ ] -------------------------------- [ ] inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage. [ ] swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes: [ ] ffff80003d7c08d0 (&v3d_priv->stats[i].lock){?.+.}-{0:0}, at: v3d_irq+0xc8/0x660 [v3d] [ ] {HARDIRQ-ON-W} state was registered at: [ ] lock_acquire+0x1f8/0x328 [ ] v3d_job_start_stats.isra.0+0xd8/0x218 [v3d] [ ] v3d_bin_job_run+0x23c/0x388 [v3d] [ ] drm_sched_run_job_work+0x520/0x6d0 [gpu_sched] [ ] process_one_work+0x62c/0xb48 [ ] worker_thread+0x468/0x5b0 [ ] kthread+0x1c4/0x1e0 [ ] ret_from_fork+0x10/0x20 [ ] irq event stamp: 337094 [ ] hardirqs last enabled at (337093): [] default_idle_call+0x11c/0x140 [ ] hardirqs last disabled at (337094): [] el1_interrupt+0x24/0x58 [ ] softirqs last enabled at (337082): [] handle_softirqs+0x4e0/0x538 [ ] softirqs last disabled at (337073): [] __do_softirq+0x1c/0x28 [ ] other info that might help us debug this: [ ] Possible unsafe locking scenario: [ ] CPU0 [ ] ---- [ ] lock(&v3d_priv->stats[i].lock); [ ] [ ] lock(&v3d_priv->stats[i].lock); [ ] *** DEADLOCK *** [ ] no locks held by swapper/0/0. [ ] stack backtrace: [ ] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G WC 6.10.3-v8-16k-numa #159 [ ] Hardware name: Raspberry Pi 5 Model B Rev 1.0 (DT) [ ] Call trace: [ ] dump_backtrace+0x170/0x1b8 [ ] show_stack+0x20/0x38 [ ] dump_stack_lvl+0xb4/0xd0 [ ] dump_stack+0x18/0x28 [ ] print_usage_bug+0x3cc/0x3f0 [ ] mark_lock+0x4d0/0x968 [ ] __lock_acquire+0x784/0x18c8 [ ] lock_acquire+0x1f8/0x328 [ ] v3d_job_update_stats+0xec/0x2e0 [v3d] [ ] v3d_irq+0xc8/0x660 [v3d] [ ] __handle_irq_event_percpu+0x1f8/0x488 [ ] handle_irq_event+0x88/0x128 [ ] handle_fasteoi_irq+0x298/0x408 [ ] generic_handle_domain_irq+0x50/0x78 But it is a false positive because all the queue-stats pairs have their own lock and jobs are also one at a time. Nevertheless we can appease lockdep by disabling local interrupts to make it see lock usage is consistent. Signed-off-by: Tvrtko Ursulin Fixes: 6abe93b621ab ("drm/v3d: Fix race-condition between sysfs/fdinfo and interrupt handler") Cc: Maíra Canal --- drivers/gpu/drm/v3d/v3d_sched.c | 46 +++++++++++++++++++++++++++++---- 1 file changed, 41 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/v3d/v3d_sched.c b/drivers/gpu/drm/v3d/v3d_sched.c index cc2e5a89467b27..e4fc3d401eddef 100644 --- a/drivers/gpu/drm/v3d/v3d_sched.c +++ b/drivers/gpu/drm/v3d/v3d_sched.c @@ -135,8 +135,31 @@ v3d_job_start_stats(struct v3d_job *job, enum v3d_queue queue) struct v3d_stats *global_stats = &v3d->queue[queue].stats; struct v3d_stats *local_stats = &file->stats[queue]; u64 now = local_clock(); - - preempt_disable(); + unsigned long flags; + + /* + * We only need to disable local interrupts to appease lockdep who + * otherwise would think v3d_job_start_stats vs v3d_stats_update has an + * unsafe in-irq vs no-irq-off usage problem. This is a false positive + * becuase all the locks are per queue and stats type, and all jobs are + * completely one at a time serialised. More specifically: + * + * 1. Locks for GPU queues are updated from interrupt handlers under a + * spin lock and started here with preemption disabled. + * + * 2. Locks for CPU queues are updated from the worker with preemption + * disabled and equally started here with preemption disabled. + * + * Therefore both are consistent. + * + * 3. Because next job can only be queued after the previous one has + * been signaled, and locks are per queue, there is also no scope for + * the start part to race with the update part. + */ + if (IS_ENABLED(CONFIG_LOCKDEP)) + local_irq_save(flags); + else + preempt_disable(); write_seqcount_begin(&local_stats->lock); local_stats->start_ns = now; @@ -146,7 +169,10 @@ v3d_job_start_stats(struct v3d_job *job, enum v3d_queue queue) global_stats->start_ns = now; write_seqcount_end(&global_stats->lock); - preempt_enable(); + if (IS_ENABLED(CONFIG_LOCKDEP)) + local_irq_restore(flags); + else + preempt_enable(); } static void @@ -167,11 +193,21 @@ v3d_job_update_stats(struct v3d_job *job, enum v3d_queue queue) struct v3d_stats *global_stats = &v3d->queue[queue].stats; struct v3d_stats *local_stats = &file->stats[queue]; u64 now = local_clock(); + unsigned long flags; + + /* See comment in v3d_job_start_stats() */ + if (IS_ENABLED(CONFIG_LOCKDEP)) + local_irq_save(flags); + else + preempt_disable(); - preempt_disable(); v3d_stats_update(local_stats, now); v3d_stats_update(global_stats, now); - preempt_enable(); + + if (IS_ENABLED(CONFIG_LOCKDEP)) + local_irq_restore(flags); + else + preempt_enable(); } static struct dma_fence *v3d_bin_job_run(struct drm_sched_job *sched_job)