From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:43066 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750844AbcEHNFI (ORCPT ); Sun, 8 May 2016 09:05:08 -0400 Subject: Patch "Drivers: hv: vmbus: Fix signaling logic in hv_need_to_signal_on_read()" has been added to the 4.5-stable tree To: kys@microsoft.com, arseneyr@microsoft.com, decui@microsoft.com, gregkh@linuxfoundation.org Cc: , From: Date: Sun, 08 May 2016 15:05:05 +0200 Message-ID: <1462712705183186@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled Drivers: hv: vmbus: Fix signaling logic in hv_need_to_signal_on_read() to the 4.5-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drivers-hv-vmbus-fix-signaling-logic-in-hv_need_to_signal_on_read.patch and it can be found in the queue-4.5 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 1db488d12894f1936360779d6ab2aede3dd7f06a Mon Sep 17 00:00:00 2001 From: "K. Y. Srinivasan" Date: Sat, 2 Apr 2016 16:17:38 -0700 Subject: Drivers: hv: vmbus: Fix signaling logic in hv_need_to_signal_on_read() From: K. Y. Srinivasan commit 1db488d12894f1936360779d6ab2aede3dd7f06a upstream. On the consumer side, we have interrupt driven flow management of the producer. It is sufficient to base the signaling decision on the amount of space that is available to write after the read is complete. The current code samples the previous available space and uses this in making the signaling decision. This state can be stale and is unnecessary. Since the state can be stale, we end up not signaling the host (when we should) and this can result in a hang. Fix this problem by removing the unnecessary check. I would like to thank Arseney Romanenko for pointing out this issue. Also, issue a full memory barrier before making the signaling descision to correctly deal with potential reordering of the write (read index) followed by the read of pending_sz. Signed-off-by: K. Y. Srinivasan Tested-by: Dexuan Cui Signed-off-by: Greg Kroah-Hartman --- drivers/hv/ring_buffer.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) --- a/drivers/hv/ring_buffer.c +++ b/drivers/hv/ring_buffer.c @@ -103,15 +103,29 @@ static bool hv_need_to_signal(u32 old_wr * there is room for the producer to send the pending packet. */ -static bool hv_need_to_signal_on_read(u32 prev_write_sz, - struct hv_ring_buffer_info *rbi) +static bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi) { u32 cur_write_sz; u32 r_size; - u32 write_loc = rbi->ring_buffer->write_index; + u32 write_loc; u32 read_loc = rbi->ring_buffer->read_index; - u32 pending_sz = rbi->ring_buffer->pending_send_sz; + u32 pending_sz; + /* + * Issue a full memory barrier before making the signaling decision. + * Here is the reason for having this barrier: + * If the reading of the pend_sz (in this function) + * were to be reordered and read before we commit the new read + * index (in the calling function) we could + * have a problem. If the host were to set the pending_sz after we + * have sampled pending_sz and go to sleep before we commit the + * read index, we could miss sending the interrupt. Issue a full + * memory barrier to address this. + */ + mb(); + + pending_sz = rbi->ring_buffer->pending_send_sz; + write_loc = rbi->ring_buffer->write_index; /* If the other end is not blocked on write don't bother. */ if (pending_sz == 0) return false; @@ -120,7 +134,7 @@ static bool hv_need_to_signal_on_read(u3 cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) : read_loc - write_loc; - if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz)) + if (cur_write_sz >= pending_sz) return true; return false; @@ -458,7 +472,7 @@ int hv_ringbuffer_read(struct hv_ring_bu /* Update the read index */ hv_set_next_read_location(inring_info, next_read_location); - *signal = hv_need_to_signal_on_read(bytes_avail_towrite, inring_info); + *signal = hv_need_to_signal_on_read(inring_info); out_unlock: spin_unlock_irqrestore(&inring_info->ring_lock, flags); Patches currently in stable-queue which might be from kys@microsoft.com are queue-4.5/drivers-hv-vmbus-fix-signaling-logic-in-hv_need_to_signal_on_read.patch