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Subject[PATCH 4.14 015/165] nbd: handle unexpected replies better
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Josef Bacik <josef@toxicpanda.com>

[ Upstream commit 8f3ea35929a0806ad1397db99a89ffee0140822a ]

If the server or network is misbehaving and we get an unexpected reply
we can sometimes miss the request not being started and wait on a
request and never get a response, or even double complete the same
request. Fix this by replacing the send_complete completion with just a
per command lock. Add a per command cookie as well so that we can know
if we're getting a double completion for a previous event. Also check
to make sure we dont have REQUEUED set as that means we raced with the
timeout handler and need to just let the retry occur.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/block/nbd.c | 75 ++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 61 insertions(+), 14 deletions(-)

--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -116,11 +116,12 @@ struct nbd_device {

struct nbd_cmd {
struct nbd_device *nbd;
+ struct mutex lock;
int index;
int cookie;
- struct completion send_complete;
blk_status_t status;
unsigned long flags;
+ u32 cmd_cookie;
};

#if IS_ENABLED(CONFIG_DEBUG_FS)
@@ -157,6 +158,27 @@ static void nbd_requeue_cmd(struct nbd_c
blk_mq_requeue_request(req, true);
}

+#define NBD_COOKIE_BITS 32
+
+static u64 nbd_cmd_handle(struct nbd_cmd *cmd)
+{
+ struct request *req = blk_mq_rq_from_pdu(cmd);
+ u32 tag = blk_mq_unique_tag(req);
+ u64 cookie = cmd->cmd_cookie;
+
+ return (cookie << NBD_COOKIE_BITS) | tag;
+}
+
+static u32 nbd_handle_to_tag(u64 handle)
+{
+ return (u32)handle;
+}
+
+static u32 nbd_handle_to_cookie(u64 handle)
+{
+ return (u32)(handle >> NBD_COOKIE_BITS);
+}
+
static const char *nbdcmd_to_ascii(int cmd)
{
switch (cmd) {
@@ -317,6 +339,9 @@ static enum blk_eh_timer_return nbd_xmit
}
config = nbd->config;

+ if (!mutex_trylock(&cmd->lock))
+ return BLK_EH_RESET_TIMER;
+
if (config->num_connections > 1) {
dev_err_ratelimited(nbd_to_dev(nbd),
"Connection timed out, retrying\n");
@@ -339,6 +364,7 @@ static enum blk_eh_timer_return nbd_xmit
nbd_mark_nsock_dead(nbd, nsock, 1);
mutex_unlock(&nsock->tx_lock);
}
+ mutex_unlock(&cmd->lock);
nbd_requeue_cmd(cmd);
nbd_config_put(nbd);
return BLK_EH_NOT_HANDLED;
@@ -349,6 +375,7 @@ static enum blk_eh_timer_return nbd_xmit
}
set_bit(NBD_TIMEDOUT, &config->runtime_flags);
cmd->status = BLK_STS_IOERR;
+ mutex_unlock(&cmd->lock);
sock_shutdown(nbd);
nbd_config_put(nbd);

@@ -425,9 +452,9 @@ static int nbd_send_cmd(struct nbd_devic
struct iov_iter from;
unsigned long size = blk_rq_bytes(req);
struct bio *bio;
+ u64 handle;
u32 type;
u32 nbd_cmd_flags = 0;
- u32 tag = blk_mq_unique_tag(req);
int sent = nsock->sent, skip = 0;

iov_iter_kvec(&from, WRITE | ITER_KVEC, &iov, 1, sizeof(request));
@@ -469,6 +496,8 @@ static int nbd_send_cmd(struct nbd_devic
goto send_pages;
}
iov_iter_advance(&from, sent);
+ } else {
+ cmd->cmd_cookie++;
}
cmd->index = index;
cmd->cookie = nsock->cookie;
@@ -477,7 +506,8 @@ static int nbd_send_cmd(struct nbd_devic
request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
request.len = htonl(size);
}
- memcpy(request.handle, &tag, sizeof(tag));
+ handle = nbd_cmd_handle(cmd);
+ memcpy(request.handle, &handle, sizeof(handle));

dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
cmd, nbdcmd_to_ascii(type),
@@ -570,10 +600,12 @@ static struct nbd_cmd *nbd_read_stat(str
struct nbd_reply reply;
struct nbd_cmd *cmd;
struct request *req = NULL;
+ u64 handle;
u16 hwq;
u32 tag;
struct kvec iov = {.iov_base = &reply, .iov_len = sizeof(reply)};
struct iov_iter to;
+ int ret = 0;

reply.magic = 0;
iov_iter_kvec(&to, READ | ITER_KVEC, &iov, 1, sizeof(reply));
@@ -591,8 +623,8 @@ static struct nbd_cmd *nbd_read_stat(str
return ERR_PTR(-EPROTO);
}

- memcpy(&tag, reply.handle, sizeof(u32));
-
+ memcpy(&handle, reply.handle, sizeof(handle));
+ tag = nbd_handle_to_tag(handle);
hwq = blk_mq_unique_tag_to_hwq(tag);
if (hwq < nbd->tag_set.nr_hw_queues)
req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
@@ -603,11 +635,25 @@ static struct nbd_cmd *nbd_read_stat(str
return ERR_PTR(-ENOENT);
}
cmd = blk_mq_rq_to_pdu(req);
+
+ mutex_lock(&cmd->lock);
+ if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
+ dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
+ req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
+ ret = -ENOENT;
+ goto out;
+ }
+ if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
+ dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
+ req);
+ ret = -ENOENT;
+ goto out;
+ }
if (ntohl(reply.error)) {
dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
ntohl(reply.error));
cmd->status = BLK_STS_IOERR;
- return cmd;
+ goto out;
}

dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", cmd);
@@ -632,18 +678,18 @@ static struct nbd_cmd *nbd_read_stat(str
if (nbd_disconnected(config) ||
config->num_connections <= 1) {
cmd->status = BLK_STS_IOERR;
- return cmd;
+ goto out;
}
- return ERR_PTR(-EIO);
+ ret = -EIO;
+ goto out;
}
dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
cmd, bvec.bv_len);
}
- } else {
- /* See the comment in nbd_queue_rq. */
- wait_for_completion(&cmd->send_complete);
}
- return cmd;
+out:
+ mutex_unlock(&cmd->lock);
+ return ret ? ERR_PTR(ret) : cmd;
}

static void recv_work(struct work_struct *work)
@@ -843,7 +889,7 @@ static blk_status_t nbd_queue_rq(struct
* that the server is misbehaving (or there was an error) before we're
* done sending everything over the wire.
*/
- init_completion(&cmd->send_complete);
+ mutex_lock(&cmd->lock);
clear_bit(NBD_CMD_REQUEUED, &cmd->flags);

/* We can be called directly from the user space process, which means we
@@ -856,7 +902,7 @@ static blk_status_t nbd_queue_rq(struct
ret = BLK_STS_IOERR;
else if (!ret)
ret = BLK_STS_OK;
- complete(&cmd->send_complete);
+ mutex_unlock(&cmd->lock);

return ret;
}
@@ -1461,6 +1507,7 @@ static int nbd_init_request(struct blk_m
struct nbd_cmd *cmd = blk_mq_rq_to_pdu(rq);
cmd->nbd = set->driver_data;
cmd->flags = 0;
+ mutex_init(&cmd->lock);
return 0;
}


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