вт, 5 мар. 2019 г. в 21:44, Ronnie Sahlberg <lsahlber@xxxxxxxxxx>:
>
> Since we can now wait for multiple requests atomically in
> wait_for_free_request() we can now greatly simplify the handling
> of the credits in this function.
>
> This fixes a potential deadlock where many concurrent compound requests
> could each have reserved 1 or 2 credits each but are all blocked
> waiting for the final credits they need to be able to issue the requests
> to the server.
>
> Set a default timeout of 60 seconds for compounded requests.
Thanks for simplifying the compound_send_recv() and adding the
timeout. Although 60sec seems rather big interval, until we have
sequential fallback, it is the best we can do I guess.
>
> Signed-off-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
> ---
> fs/cifs/transport.c | 82 ++++++++++++++---------------------------------------
> 1 file changed, 21 insertions(+), 61 deletions(-)
>
> diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
> index 3263e8b3a57d..f759822dd2f2 100644
> --- a/fs/cifs/transport.c
> +++ b/fs/cifs/transport.c
> @@ -592,6 +592,14 @@ wait_for_free_request(struct TCP_Server_Info *server, const int flags,
> instance);
> }
>
> +static int
> +wait_for_compound_request(struct TCP_Server_Info *server, int num,
> + const int flags, unsigned int *instance)
> +{
> + return wait_for_free_credits(server, num, 60000, flags,
> + instance);
> +}
> +
> int
> cifs_wait_mtu_credits(struct TCP_Server_Info *server, unsigned int size,
> unsigned int *num, struct cifs_credits *credits)
> @@ -920,7 +928,6 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
> { .value = 0, .instance = 0 }
> };
> unsigned int instance;
> - unsigned int first_instance = 0;
> char *buf;
>
> optype = flags & CIFS_OP_MASK;
> @@ -946,70 +953,27 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
> spin_unlock(&ses->server->req_lock);
> return -ENOTSUPP;
The code above could also be moved into wait_for_free_credits() to
make compound_send_recv() even smaller.
> }
> - } else {
> - /* enough credits to send the whole compounded request */
> - ses->server->credits -= num_rqst;
> - ses->server->in_flight += num_rqst;
> - first_instance = ses->server->reconnect_instance;
> }
> spin_unlock(&ses->server->req_lock);
>
> - if (first_instance) {
> - cifs_dbg(FYI, "Acquired %d credits at once\n", num_rqst);
> - for (i = 0; i < num_rqst; i++) {
> - credits[i].value = 1;
> - credits[i].instance = first_instance;
> - }
> - goto setup_rqsts;
> - }
> -
> /*
> - * There are not enough credits to send the whole compound request but
> - * there are requests in flight that may bring credits from the server.
> + * Wait for all the requests to become available.
> * This approach still leaves the possibility to be stuck waiting for
> * credits if the server doesn't grant credits to the outstanding
> - * requests. This should be fixed by returning immediately and letting
> - * a caller fallback to sequential commands instead of compounding.
> - * Ensure we obtain 1 credit per request in the compound chain.
> + * requests and if the client is completely idle, not generating any
> + * other requests.
> + * This can be handled by the eventual session reconnect.
> */
> - for (i = 0; i < num_rqst; i++) {
> - rc = wait_for_free_request(ses->server, flags, &instance);
> -
> - if (rc == 0) {
> - credits[i].value = 1;
> - credits[i].instance = instance;
> - /*
> - * All parts of the compound chain must get credits from
> - * the same session, otherwise we may end up using more
> - * credits than the server granted. If there were
> - * reconnects in between, return -EAGAIN and let callers
> - * handle it.
> - */
> - if (i == 0)
> - first_instance = instance;
> - else if (first_instance != instance) {
> - i++;
> - rc = -EAGAIN;
> - }
> - }
> + rc = wait_for_compound_request(ses->server, num_rqst, flags,
> + &instance);
> + if (rc)
> + return rc;
>
> - if (rc) {
> - /*
> - * We haven't sent an SMB packet to the server yet but
> - * we already obtained credits for i requests in the
> - * compound chain - need to return those credits back
> - * for future use. Note that we need to call add_credits
> - * multiple times to match the way we obtained credits
> - * in the first place and to account for in flight
> - * requests correctly.
> - */
> - for (j = 0; j < i; j++)
> - add_credits(ses->server, &credits[j], optype);
> - return rc;
> - }
> + for (i = 0; i < num_rqst; i++) {
> + credits[i].value = 1;
> + credits[i].instance = instance;
> }
>
> -setup_rqsts:
> /*
> * Make sure that we sign in the same order that we send on this socket
> * and avoid races inside tcp sendmsg code that could cause corruption
> @@ -1020,17 +984,13 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
>
> /*
> * All the parts of the compound chain belong obtained credits from the
> - * same session (see the appropriate checks above). In the same time
> - * there might be reconnects after those checks but before we acquired
> - * the srv_mutex. We can not use credits obtained from the previous
> + * same session. We can not use credits obtained from the previous
> * session to send this request. Check if there were reconnects after
> * we obtained credits and return -EAGAIN in such cases to let callers
> * handle it.
> */
> - if (first_instance != ses->server->reconnect_instance) {
> + if (instance != ses->server->reconnect_instance) {
> mutex_unlock(&ses->server->srv_mutex);
> - for (j = 0; j < num_rqst; j++)
> - add_credits(ses->server, &credits[j], optype);
Why removing this? We obtained credits and increased the number of
requests in flight but are about to return without sending the request
- need to return those credits back and adjust the number of requests
in flight.
I understand it may be confusing because the session changed and
add_credits won't actually add any credits *but* it will adjust the
number of requests in flight and possibly re-balance the remaining
credits in the current session, thus it is still needed to call
add_credits for all parts of compound chain here.
> return -EAGAIN;
> }
>
> --
> 2.13.6
>
--
Best regards,
Pavel Shilovsky
