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patch "mei: remove support for broken parallel read" added to char-misc-next

PATCH [email protected] 1 participant 1 message Feb 11, 2017

Subsystems (3)
Stable branch Char and misc drivers Intel management engine (mei)
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This is a note to let you know that I've just added the patch titled

mei: remove support for broken parallel read

to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

Quoted 1 line

From cb97fbbcac15982406e0c74cd5512a8b6fcf10b3 Mon Sep 17 00:00:00 2001

From: Alexander Usyskin <[email protected]>
Date: Wed, 8 Feb 2017 00:41:45 +0200
Subject: mei: remove support for broken parallel read

Parallel reads from multiple threads on a file descriptor are not well defined and racy. It is safer to return to original behavior and simply fail the additional read.
The solution is to remove request for next read credit.

Cc <[email protected]> #4.9
Fixes ff1586a7ea57 ("mei: enqueue consecutive reads")
Signed-off-by Alexander Usyskin <[email protected]>
Signed-off-by Tomas Winkler <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 drivers/misc/mei/main.c | 48 ++++++++++++++++++++++++++----------------------
 1 file changed, 26 insertions(+), 22 deletions(-)
drivers/misc/mei/main.c +26 -22
index e1bf54481fd6..9d0b7050c79a 100644
@@ -182,32 +182,36 @@ static ssize_t mei_read(struct file *file, char __user *ubuf,
 		goto out;
 	}
 
-	if (rets == -EBUSY &&
-	    !mei_cl_enqueue_ctrl_wr_cb(cl, length, MEI_FOP_READ, file)) {
-		rets = -ENOMEM;
-		goto out;
-	}
 
-	do {
-		mutex_unlock(&dev->device_lock);
-
-		if (wait_event_interruptible(cl->rx_wait,
-					     (!list_empty(&cl->rd_completed)) ||
-					     (!mei_cl_is_connected(cl)))) {
+again:
+	mutex_unlock(&dev->device_lock);
+	if (wait_event_interruptible(cl->rx_wait,
+				     !list_empty(&cl->rd_completed) ||
+				     !mei_cl_is_connected(cl))) {
+		if (signal_pending(current))
+			return -EINTR;
+		return -ERESTARTSYS;
+	}
+	mutex_lock(&dev->device_lock);
 
-			if (signal_pending(current))
-				return -EINTR;
-			return -ERESTARTSYS;
-		}
+	if (!mei_cl_is_connected(cl)) {
+		rets = -ENODEV;
+		goto out;
+	}
 
-		mutex_lock(&dev->device_lock);
-		if (!mei_cl_is_connected(cl)) {
-			rets = -ENODEV;
-			goto out;
-		}
+	cb = mei_cl_read_cb(cl, file);
+	if (!cb) {
+		/*
+		 * For amthif all the waiters are woken up,
+		 * but only fp with matching cb->fp get the cb,
+		 * the others have to return to wait on read.
+		 */
+		if (cl == &dev->iamthif_cl)
+			goto again;
 
-		cb = mei_cl_read_cb(cl, file);
-	} while (!cb);
+		rets = 0;
+		goto out;
+	}
 
 copy_buffer:
 	/* now copy the data to user space */
Signature · 1 line
2.11.1