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From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org,
	linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Carsten Emde <C.Emde@osadl.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	John Kacur <jkacur@redhat.com>, Julia Cartwright <julia@ni.com>,
	Daniel Wagner <wagi@monom.org>, Tom Zanussi <zanussi@kernel.org>
Subject: [PATCH RT 05/30] dma-buf: Use seqlock_t instread disabling preemption
Date: Thu, 23 Jan 2020 15:39:35 -0500
Message-ID: <20200123203943.036685630@goodmis.org> (raw)
In-Reply-To: <20200123203930.646725253@goodmis.org>

4.19.94-rt39-rc2 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

[ Upstream commit 240610aa31094f51f299f06eb8dae8d4cd8d4500 ]

"dma reservation" disables preemption while acquiring the write access
for "seqcount" and then may acquire a spinlock_t.

Replace the seqcount with a seqlock_t which provides seqcount like
semantic and lock for writer.

Link: https://lkml.kernel.org/r/f410b429-db86-f81c-7c67-f563fa808b62@free.fr
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 drivers/dma-buf/dma-buf.c                     |  8 ++--
 drivers/dma-buf/reservation.c                 | 43 +++++++------------
 .../gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c  |  6 +--
 drivers/gpu/drm/i915/i915_gem.c               | 10 ++---
 include/linux/reservation.h                   |  4 +-
 5 files changed, 29 insertions(+), 42 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 69842145c223..4c3ef46e7149 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -179,7 +179,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
 		return 0;
 
 retry:
-	seq = read_seqcount_begin(&resv->seq);
+	seq = read_seqbegin(&resv->seq);
 	rcu_read_lock();
 
 	fobj = rcu_dereference(resv->fence);
@@ -188,7 +188,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
 	else
 		shared_count = 0;
 	fence_excl = rcu_dereference(resv->fence_excl);
-	if (read_seqcount_retry(&resv->seq, seq)) {
+	if (read_seqretry(&resv->seq, seq)) {
 		rcu_read_unlock();
 		goto retry;
 	}
@@ -1046,12 +1046,12 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
 
 		robj = buf_obj->resv;
 		while (true) {
-			seq = read_seqcount_begin(&robj->seq);
+			seq = read_seqbegin(&robj->seq);
 			rcu_read_lock();
 			fobj = rcu_dereference(robj->fence);
 			shared_count = fobj ? fobj->shared_count : 0;
 			fence = rcu_dereference(robj->fence_excl);
-			if (!read_seqcount_retry(&robj->seq, seq))
+			if (!read_seqretry(&robj->seq, seq))
 				break;
 			rcu_read_unlock();
 		}
diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index 49ab09468ba1..f11d58492216 100644
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -109,8 +109,7 @@ reservation_object_add_shared_inplace(struct reservation_object *obj,
 
 	dma_fence_get(fence);
 
-	preempt_disable();
-	write_seqcount_begin(&obj->seq);
+	write_seqlock(&obj->seq);
 
 	for (i = 0; i < fobj->shared_count; ++i) {
 		struct dma_fence *old_fence;
@@ -121,8 +120,7 @@ reservation_object_add_shared_inplace(struct reservation_object *obj,
 		if (old_fence->context == fence->context) {
 			/* memory barrier is added by write_seqcount_begin */
 			RCU_INIT_POINTER(fobj->shared[i], fence);
-			write_seqcount_end(&obj->seq);
-			preempt_enable();
+			write_sequnlock(&obj->seq);
 
 			dma_fence_put(old_fence);
 			return;
@@ -146,8 +144,7 @@ reservation_object_add_shared_inplace(struct reservation_object *obj,
 		fobj->shared_count++;
 	}
 
-	write_seqcount_end(&obj->seq);
-	preempt_enable();
+	write_sequnlock(&obj->seq);
 
 	dma_fence_put(signaled);
 }
@@ -191,15 +188,13 @@ reservation_object_add_shared_replace(struct reservation_object *obj,
 	fobj->shared_count++;
 
 done:
-	preempt_disable();
-	write_seqcount_begin(&obj->seq);
+	write_seqlock(&obj->seq);
 	/*
 	 * RCU_INIT_POINTER can be used here,
 	 * seqcount provides the necessary barriers
 	 */
 	RCU_INIT_POINTER(obj->fence, fobj);
-	write_seqcount_end(&obj->seq);
-	preempt_enable();
+	write_sequnlock(&obj->seq);
 
 	if (!old)
 		return;
@@ -259,14 +254,11 @@ void reservation_object_add_excl_fence(struct reservation_object *obj,
 	if (fence)
 		dma_fence_get(fence);
 
-	preempt_disable();
-	write_seqcount_begin(&obj->seq);
-	/* write_seqcount_begin provides the necessary memory barrier */
+	write_seqlock(&obj->seq);
 	RCU_INIT_POINTER(obj->fence_excl, fence);
 	if (old)
 		old->shared_count = 0;
-	write_seqcount_end(&obj->seq);
-	preempt_enable();
+	write_sequnlock(&obj->seq);
 
 	/* inplace update, no shared fences */
 	while (i--)
@@ -349,13 +341,10 @@ int reservation_object_copy_fences(struct reservation_object *dst,
 	src_list = reservation_object_get_list(dst);
 	old = reservation_object_get_excl(dst);
 
-	preempt_disable();
-	write_seqcount_begin(&dst->seq);
-	/* write_seqcount_begin provides the necessary memory barrier */
+	write_seqlock(&dst->seq);
 	RCU_INIT_POINTER(dst->fence_excl, new);
 	RCU_INIT_POINTER(dst->fence, dst_list);
-	write_seqcount_end(&dst->seq);
-	preempt_enable();
+	write_sequnlock(&dst->seq);
 
 	if (src_list)
 		kfree_rcu(src_list, rcu);
@@ -396,7 +385,7 @@ int reservation_object_get_fences_rcu(struct reservation_object *obj,
 		shared_count = i = 0;
 
 		rcu_read_lock();
-		seq = read_seqcount_begin(&obj->seq);
+		seq = read_seqbegin(&obj->seq);
 
 		fence_excl = rcu_dereference(obj->fence_excl);
 		if (fence_excl && !dma_fence_get_rcu(fence_excl))
@@ -445,7 +434,7 @@ int reservation_object_get_fences_rcu(struct reservation_object *obj,
 			}
 		}
 
-		if (i != shared_count || read_seqcount_retry(&obj->seq, seq)) {
+		if (i != shared_count || read_seqretry(&obj->seq, seq)) {
 			while (i--)
 				dma_fence_put(shared[i]);
 			dma_fence_put(fence_excl);
@@ -494,7 +483,7 @@ long reservation_object_wait_timeout_rcu(struct reservation_object *obj,
 
 retry:
 	shared_count = 0;
-	seq = read_seqcount_begin(&obj->seq);
+	seq = read_seqbegin(&obj->seq);
 	rcu_read_lock();
 	i = -1;
 
@@ -541,7 +530,7 @@ long reservation_object_wait_timeout_rcu(struct reservation_object *obj,
 
 	rcu_read_unlock();
 	if (fence) {
-		if (read_seqcount_retry(&obj->seq, seq)) {
+		if (read_seqretry(&obj->seq, seq)) {
 			dma_fence_put(fence);
 			goto retry;
 		}
@@ -597,7 +586,7 @@ bool reservation_object_test_signaled_rcu(struct reservation_object *obj,
 retry:
 	ret = true;
 	shared_count = 0;
-	seq = read_seqcount_begin(&obj->seq);
+	seq = read_seqbegin(&obj->seq);
 
 	if (test_all) {
 		unsigned i;
@@ -618,7 +607,7 @@ bool reservation_object_test_signaled_rcu(struct reservation_object *obj,
 				break;
 		}
 
-		if (read_seqcount_retry(&obj->seq, seq))
+		if (read_seqretry(&obj->seq, seq))
 			goto retry;
 	}
 
@@ -631,7 +620,7 @@ bool reservation_object_test_signaled_rcu(struct reservation_object *obj,
 			if (ret < 0)
 				goto retry;
 
-			if (read_seqcount_retry(&obj->seq, seq))
+			if (read_seqretry(&obj->seq, seq))
 				goto retry;
 		}
 	}
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
index f92597c292fe..10c675850aac 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -261,11 +261,9 @@ static int amdgpu_amdkfd_remove_eviction_fence(struct amdgpu_bo *bo,
 	}
 
 	/* Install the new fence list, seqcount provides the barriers */
-	preempt_disable();
-	write_seqcount_begin(&resv->seq);
+	write_seqlock(&resv->seq);
 	RCU_INIT_POINTER(resv->fence, new);
-	write_seqcount_end(&resv->seq);
-	preempt_enable();
+	write_sequnlock(&resv->seq);
 
 	/* Drop the references to the removed fences or move them to ef_list */
 	for (i = j, k = 0; i < old->shared_count; ++i) {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index c7d05ac7af3c..d484e79316bf 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -516,7 +516,7 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 				 long timeout,
 				 struct intel_rps_client *rps_client)
 {
-	unsigned int seq = __read_seqcount_begin(&resv->seq);
+	unsigned int seq = read_seqbegin(&resv->seq);
 	struct dma_fence *excl;
 	bool prune_fences = false;
 
@@ -569,9 +569,9 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 	 * signaled and that the reservation object has not been changed (i.e.
 	 * no new fences have been added).
 	 */
-	if (prune_fences && !__read_seqcount_retry(&resv->seq, seq)) {
+	if (prune_fences && !read_seqretry(&resv->seq, seq)) {
 		if (reservation_object_trylock(resv)) {
-			if (!__read_seqcount_retry(&resv->seq, seq))
+			if (!read_seqretry(&resv->seq, seq))
 				reservation_object_add_excl_fence(resv, NULL);
 			reservation_object_unlock(resv);
 		}
@@ -4615,7 +4615,7 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
 	 *
 	 */
 retry:
-	seq = raw_read_seqcount(&obj->resv->seq);
+	seq = read_seqbegin(&obj->resv->seq);
 
 	/* Translate the exclusive fence to the READ *and* WRITE engine */
 	args->busy = busy_check_writer(rcu_dereference(obj->resv->fence_excl));
@@ -4633,7 +4633,7 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
 		}
 	}
 
-	if (args->busy && read_seqcount_retry(&obj->resv->seq, seq))
+	if (args->busy && read_seqretry(&obj->resv->seq, seq))
 		goto retry;
 
 	err = 0;
diff --git a/include/linux/reservation.h b/include/linux/reservation.h
index 02166e815afb..0b31df1af698 100644
--- a/include/linux/reservation.h
+++ b/include/linux/reservation.h
@@ -72,7 +72,7 @@ struct reservation_object_list {
  */
 struct reservation_object {
 	struct ww_mutex lock;
-	seqcount_t seq;
+	seqlock_t seq;
 
 	struct dma_fence __rcu *fence_excl;
 	struct reservation_object_list __rcu *fence;
@@ -92,7 +92,7 @@ reservation_object_init(struct reservation_object *obj)
 {
 	ww_mutex_init(&obj->lock, &reservation_ww_class);
 
-	__seqcount_init(&obj->seq, reservation_seqcount_string, &reservation_seqcount_class);
+	seqlock_init(&obj->seq);
 	RCU_INIT_POINTER(obj->fence, NULL);
 	RCU_INIT_POINTER(obj->fence_excl, NULL);
 	obj->staged = NULL;
-- 
2.24.1



  parent reply index

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-23 20:39 [PATCH RT 00/30] Linux 4.19.94-rt39-rc2 Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 01/30] i2c: exynos5: Remove IRQF_ONESHOT Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 02/30] i2c: hix5hd2: " Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 03/30] sched/deadline: Ensure inactive_timer runs in hardirq context Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 04/30] thermal/x86_pkg_temp: make pkg_temp_lock a raw spinlock Steven Rostedt
2020-01-23 20:39 ` Steven Rostedt [this message]
2020-01-23 20:39 ` [PATCH RT 06/30] KVM: arm/arm64: Let the timer expire in hardirq context on RT Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 07/30] x86: preempt: Check preemption level before looking at lazy-preempt Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 08/30] hrtimer: Use READ_ONCE to access timer->base in hrimer_grab_expiry_lock() Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 09/30] hrtimer: Dont grab the expiry lock for non-soft hrtimer Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 10/30] hrtimer: Prevent using hrtimer_grab_expiry_lock() on migration_base Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 11/30] hrtimer: Add a missing bracket and hide `migration_base on !SMP Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 12/30] posix-timers: Unlock expiry lock in the early return Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 14/30] sched: __set_cpus_allowed_ptr: Check cpus_mask, not cpus_ptr Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 15/30] sched: Remove dead __migrate_disabled() check Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 16/30] sched: migrate disable: Protect cpus_ptr with lock Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 17/30] lib/smp_processor_id: Dont use cpumask_equal() Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 18/30] futex: Make the futex_hash_bucket spinlock_t again and bring back its old state Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 19/30] locking/rtmutex: Clean ->pi_blocked_on in the error case Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 20/30] lib/ubsan: Dont seralize UBSAN report Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 21/30] kmemleak: Change the lock of kmemleak_object to raw_spinlock_t Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 22/30] sched: migrate_enable: Use select_fallback_rq() Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 23/30] sched: Lazy migrate_disable processing Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 24/30] sched: migrate_enable: Use stop_one_cpu_nowait() Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 25/30] Revert "ARM: Initialize split page table locks for vector page" Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 26/30] locking: Make spinlock_t and rwlock_t a RCU section on RT Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 27/30] sched/core: migrate_enable() must access takedown_cpu_task on !HOTPLUG_CPU Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 28/30] lib/smp_processor_id: Adjust check_preemption_disabled() Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 29/30] sched: migrate_enable: Busy loop until the migration request is completed Steven Rostedt
2020-01-23 20:40 ` [PATCH RT 30/30] Linux 4.19.94-rt39-rc2 Steven Rostedt

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