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Aaron Knister
816e846c2e
Inside of start_xmit() the call to check if the connection is up and the
queueing of the packets for later transmission is not atomic which leaves
a window where cm_rep_handler can run, set the connection up, dequeue
pending packets and leave the subsequently queued packets by start_xmit()
sitting on neigh->queue until they're dropped when the connection is torn
down. This only applies to connected mode. These dropped packets can
really upset TCP, for example, and cause multi-minute delays in
transmission for open connections.
Here's the code in start_xmit where we check to see if the connection is
up:
if (ipoib_cm_get(neigh)) {
if (ipoib_cm_up(neigh)) {
ipoib_cm_send(dev, skb, ipoib_cm_get(neigh));
goto unref;
}
}
The race occurs if cm_rep_handler execution occurs after the above
connection check (specifically if it gets to the point where it acquires
priv->lock to dequeue pending skb's) but before the below code snippet in
start_xmit where packets are queued.
if (skb_queue_len(&neigh->queue) < IPOIB_MAX_PATH_REC_QUEUE) {
push_pseudo_header(skb, phdr->hwaddr);
spin_lock_irqsave(&priv->lock, flags);
__skb_queue_tail(&neigh->queue, skb);
spin_unlock_irqrestore(&priv->lock, flags);
} else {
++dev->stats.tx_dropped;
dev_kfree_skb_any(skb);
}
The patch acquires the netif tx lock in cm_rep_handler for the section
where it sets the connection up and dequeues and retransmits deferred
skb's.
Fixes: 839fcaba35 ("IPoIB: Connected mode experimental support")
Cc: stable@vger.kernel.org
Signed-off-by: Aaron Knister <aaron.s.knister@nasa.gov>
Tested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.