From 268e526b935e794386d75025577b745e6bd57f13 Mon Sep 17 00:00:00 2001
From: Mikhail Kshevetskiy <mikhail.kshevetskiy@gmail.com>
Date: Fri, 23 Sep 2011 19:22:56 +0400
Subject: [PATCH] tty/n_gsm: avoid fifo overflow in gsm_dlci_data_output
n_gsm use a simple approach: every writing to fifo correspond exactly one
reading from fifo. There are no problem in this approach until we read
less bytes then we write. As result fifo may owerflow. This leads to packet
loss and very slow responce.
For example, this happens with ping packets (about 96 byte each) and default
gsm->mtu = 64. As result we get 50 sec ping timeout and 20% packet loss.
Fix the problem by reading and sending all data from the fifo
Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
drivers/tty/n_gsm.c | 58 ++++++++++++++++++++++++---------------------
1 file changed, 31 insertions(+), 27 deletions(-)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 14c26cdd8aca2..4cb0d0a3e57b7 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -809,37 +809,41 @@ static int gsm_dlci_data_output(struct gsm_mux *gsm, struct gsm_dlci *dlci)
{
struct gsm_msg *msg;
u8 *dp;
- int len, size;
+ int len, total_size, size;
int h = dlci->adaption - 1;
- len = kfifo_len(dlci->fifo);
- if (len == 0)
- return 0;
-
- /* MTU/MRU count only the data bits */
- if (len > gsm->mtu)
- len = gsm->mtu;
-
- size = len + h;
-
- msg = gsm_data_alloc(gsm, dlci->addr, size, gsm->ftype);
- /* FIXME: need a timer or something to kick this so it can't
- get stuck with no work outstanding and no buffer free */
- if (msg == NULL)
- return -ENOMEM;
- dp = msg->data;
- switch (dlci->adaption) {
- case 1: /* Unstructured */
- break;
- case 2: /* Unstructed with modem bits. Always one byte as we never
- send inline break data */
- *dp++ = gsm_encode_modem(dlci);
- break;
+ total_size = 0;
+ while(1) {
+ len = kfifo_len(dlci->fifo);
+ if (len == 0)
+ return total_size;
+
+ /* MTU/MRU count only the data bits */
+ if (len > gsm->mtu)
+ len = gsm->mtu;
+
+ size = len + h;
+
+ msg = gsm_data_alloc(gsm, dlci->addr, size, gsm->ftype);
+ /* FIXME: need a timer or something to kick this so it can't
+ get stuck with no work outstanding and no buffer free */
+ if (msg == NULL)
+ return -ENOMEM;
+ dp = msg->data;
+ switch (dlci->adaption) {
+ case 1: /* Unstructured */
+ break;
+ case 2: /* Unstructed with modem bits. Always one byte as we never
+ send inline break data */
+ *dp++ = gsm_encode_modem(dlci);
+ break;
+ }
+ WARN_ON(kfifo_out_locked(dlci->fifo, dp , len, &dlci->lock) != len);
+ __gsm_data_queue(dlci, msg);
+ total_size += size;
}
- WARN_ON(kfifo_out_locked(dlci->fifo, dp , len, &dlci->lock) != len);
- __gsm_data_queue(dlci, msg);
/* Bytes of data we used up */
- return size;
+ return total_size;
}
/**
--
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