6.11-stable review patch. If anyone has any objections, please let me know.
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From: Tvrtko Ursulin tvrtko.ursulin@igalia.com
[ Upstream commit 06c3c406850e5495bb56ccf624d0c9477e1ba901 ]
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): [<ffffc0008144ce7c>] default_idle_call+0x11c/0x140 [ ] hardirqs last disabled at (337094): [<ffffc0008144a354>] el1_interrupt+0x24/0x58 [ ] softirqs last enabled at (337082): [<ffffc00080061d90>] handle_softirqs+0x4e0/0x538 [ ] softirqs last disabled at (337073): [<ffffc00080010364>] __do_softirq+0x1c/0x28 [ ] other info that might help us debug this: [ ] Possible unsafe locking scenario:
[ ] CPU0 [ ] ---- [ ] lock(&v3d_priv->stats[i].lock); [ ] <Interrupt> [ ] 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.
Cc: Maíra Canal mcanal@igalia.com Fixes: 6abe93b621ab ("drm/v3d: Fix race-condition between sysfs/fdinfo and interrupt handler") Signed-off-by: Tvrtko Ursulin tvrtko.ursulin@igalia.com Signed-off-by: Maíra Canal mcanal@igalia.com Link: https://patchwork.freedesktop.org/patch/msgid/20240813102505.80512-2-tursuli... Signed-off-by: Sasha Levin sashal@kernel.org --- 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 ad1e6236ff6ff..255bd9100c78a 100644 --- a/drivers/gpu/drm/v3d/v3d_sched.c +++ b/drivers/gpu/drm/v3d/v3d_sched.c @@ -133,8 +133,31 @@ 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 + * because 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; @@ -144,7 +167,10 @@ 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 @@ -165,11 +191,21 @@ 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)