[PATCH v2 2/2] drm/xe/oa: Fix locking for stream->pollin

[Ashutosh Dixit]

Previously locking was skipped for stream->pollin. This "mostly" worked
because pollin is u32/bool, even when stream->pollin is accessed
concurrently in multiple threads. However, with stream->pollin moving under
stream->oa_buffer.ptr_lock in this series, implement the correct way to
access stream->pollin, which is to access it under
stream->oa_buffer.ptr_lock.

v2: Update commit message to explain the "why" of this change (Rodrigo)
    Document the change in scope for stream->oa_buffer.ptr_lock (Rodrigo)

Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
---
 drivers/gpu/drm/xe/xe_oa.c       | 6 ++++++
 drivers/gpu/drm/xe/xe_oa_types.h | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_oa.c b/drivers/gpu/drm/xe/xe_oa.c
index fa873f3d0a9d1..9de62ce4b9e42 100644
--- a/drivers/gpu/drm/xe/xe_oa.c
+++ b/drivers/gpu/drm/xe/xe_oa.c
@@ -530,6 +530,7 @@ static ssize_t xe_oa_read(struct file *file, char __user *buf,
 			  size_t count, loff_t *ppos)
 {
 	struct xe_oa_stream *stream = file->private_data;
+	unsigned long flags;
 	size_t offset = 0;
 	int ret;
 
@@ -562,8 +563,10 @@ static ssize_t xe_oa_read(struct file *file, char __user *buf,
 	 * Also in case of -EIO, we have already waited for data before returning
 	 * -EIO, so need to wait again
 	 */
+	spin_lock_irqsave(&stream->oa_buffer.ptr_lock, flags);
 	if (ret != -ENOSPC && ret != -EIO)
 		stream->pollin = false;
+	spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags);
 
 	/* Possible values for ret are 0, -EFAULT, -ENOSPC, -EIO, -EINVAL, ... */
 	return offset ?: (ret ?: -EAGAIN);
@@ -573,6 +576,7 @@ static __poll_t xe_oa_poll_locked(struct xe_oa_stream *stream,
 				  struct file *file, poll_table *wait)
 {
 	__poll_t events = 0;
+	unsigned long flags;
 
 	poll_wait(file, &stream->poll_wq, wait);
 
@@ -582,8 +586,10 @@ static __poll_t xe_oa_poll_locked(struct xe_oa_stream *stream,
 	 * in use. We rely on hrtimer xe_oa_poll_check_timer_cb to notify us when there
 	 * are samples to read
 	 */
+	spin_lock_irqsave(&stream->oa_buffer.ptr_lock, flags);
 	if (stream->pollin)
 		events |= EPOLLIN;
+	spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags);
 
 	return events;
 }
diff --git a/drivers/gpu/drm/xe/xe_oa_types.h b/drivers/gpu/drm/xe/xe_oa_types.h
index 52e33c37d5ee8..5c4ea13f646fc 100644
--- a/drivers/gpu/drm/xe/xe_oa_types.h
+++ b/drivers/gpu/drm/xe/xe_oa_types.h
@@ -159,7 +159,7 @@ struct xe_oa_buffer {
 	/** @vaddr: mapped vaddr of the OA buffer */
 	u8 *vaddr;
 
-	/** @ptr_lock: Lock protecting reads/writes to head/tail pointers */
+	/** @ptr_lock: Lock protecting reads/writes to head/tail pointers and stream->pollin */
 	spinlock_t ptr_lock;
 
 	/** @head: Cached head to read from */
-- 
2.47.1