FAILED: patch "[PATCH] dma-buf/poll: Get a file reference for outstanding fence" failed to apply to 5.15-stable tree

PATCH [email protected] 1 participant 1 message Nov 22, 2021

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Stable branch DMA buffer sharing framework

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2021-11-22 13:06 UTC #0 lore raw

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ff2d23843f7fb4f13055be5a4a9a20ddd04e6e9c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michel=20D=C3=A4nzer?= <[email protected]>
Date: Fri, 23 Jul 2021 09:58:57 +0200
Subject: [PATCH] dma-buf/poll: Get a file reference for outstanding fence
callbacks
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This makes sure we don't hit the

	BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active);

in dma_buf_release, which could be triggered by user space closing the dma-buf file description while there are outstanding fence callbacks from dma_buf_poll.

Cc [email protected]

Signed-off-by Michel Dänzer <[email protected]>

Reviewed-by Christian König <[email protected]>

Link https://patchwork.freedesktop.org/patch/msgid/[email protected]

Signed-off-by Christian König <[email protected]>

drivers/dma-buf/dma-buf.c +12 -6

index beb504a92d60..35fe1cb5ad98 100644
@@ -67,12 +67,9 @@ static void dma_buf_release(struct dentry *dentry)
 	BUG_ON(dmabuf->vmapping_counter);
 
 	/*
-	 * Any fences that a dma-buf poll can wait on should be signaled
-	 * before releasing dma-buf. This is the responsibility of each
-	 * driver that uses the reservation objects.
-	 *
-	 * If you hit this BUG() it means someone dropped their ref to the
-	 * dma-buf while still having pending operation to the buffer.
+	 * If you hit this BUG() it could mean:
+	 * * There's a file reference imbalance in dma_buf_poll / dma_buf_poll_cb or somewhere else
+	 * * dmabuf->cb_in/out.active are non-0 despite no pending fence callback
 	 */
 	BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active);

@@ -200,6 +197,7 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
 static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
 {
 	struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb;
+	struct dma_buf *dmabuf = container_of(dcb->poll, struct dma_buf, poll);
 	unsigned long flags;
 
 	spin_lock_irqsave(&dcb->poll->lock, flags);

@@ -207,6 +205,8 @@ static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
 	dcb->active = 0;
 	spin_unlock_irqrestore(&dcb->poll->lock, flags);
 	dma_fence_put(fence);
+	/* Paired with get_file in dma_buf_poll */
+	fput(dmabuf->file);
 }
 
 static bool dma_buf_poll_add_cb(struct dma_resv *resv, bool write,

@@ -259,6 +259,9 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
 		spin_unlock_irq(&dmabuf->poll.lock);
 
 		if (events & EPOLLOUT) {
+			/* Paired with fput in dma_buf_poll_cb */
+			get_file(dmabuf->file);
+
 			if (!dma_buf_poll_add_cb(resv, true, dcb))
 				/* No callback queued, wake up any other waiters */
 				dma_buf_poll_cb(NULL, &dcb->cb);

@@ -279,6 +282,9 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
 		spin_unlock_irq(&dmabuf->poll.lock);
 
 		if (events & EPOLLIN) {
+			/* Paired with fput in dma_buf_poll_cb */
+			get_file(dmabuf->file);
+
 			if (!dma_buf_poll_add_cb(resv, false, dcb))
 				/* No callback queued, wake up any other waiters */
 				dma_buf_poll_cb(NULL, &dcb->cb);