From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Ronnie Sahlberg <lsahlber@redhat.com>,
Pavel Shilovsky <pshilov@microsoft.com>,
Steve French <stfrench@microsoft.com>,
Sasha Levin <sashal@kernel.org>,
linux-cifs@vger.kernel.org
Subject: [PATCH AUTOSEL 5.2 31/85] cifs: Fix a race condition with cifs_echo_request
Date: Fri, 26 Jul 2019 09:38:41 -0400 [thread overview]
Message-ID: <20190726133936.11177-31-sashal@kernel.org> (raw)
In-Reply-To: <20190726133936.11177-1-sashal@kernel.org>
From: Ronnie Sahlberg <lsahlber@redhat.com>
[ Upstream commit f2caf901c1b7ce65f9e6aef4217e3241039db768 ]
There is a race condition with how we send (or supress and don't send)
smb echos that will cause the client to incorrectly think the
server is unresponsive and thus needs to be reconnected.
Summary of the race condition:
1) Daisy chaining scheduling creates a gap.
2) If traffic comes unfortunate shortly after
the last echo, the planned echo is suppressed.
3) Due to the gap, the next echo transmission is delayed
until after the timeout, which is set hard to twice
the echo interval.
This is fixed by changing the timeouts from 2 to three times the echo interval.
Detailed description of the bug: https://lutz.donnerhacke.de/eng/Blog/Groundhog-Day-with-SMB-remount
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/cifs/connect.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 8dd6637a3cbb..0872188ce3c6 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -706,10 +706,10 @@ static bool
server_unresponsive(struct TCP_Server_Info *server)
{
/*
- * We need to wait 2 echo intervals to make sure we handle such
+ * We need to wait 3 echo intervals to make sure we handle such
* situations right:
* 1s client sends a normal SMB request
- * 2s client gets a response
+ * 3s client gets a response
* 30s echo workqueue job pops, and decides we got a response recently
* and don't need to send another
* ...
@@ -718,9 +718,9 @@ server_unresponsive(struct TCP_Server_Info *server)
*/
if ((server->tcpStatus == CifsGood ||
server->tcpStatus == CifsNeedNegotiate) &&
- time_after(jiffies, server->lstrp + 2 * server->echo_interval)) {
+ time_after(jiffies, server->lstrp + 3 * server->echo_interval)) {
cifs_dbg(VFS, "Server %s has not responded in %lu seconds. Reconnecting...\n",
- server->hostname, (2 * server->echo_interval) / HZ);
+ server->hostname, (3 * server->echo_interval) / HZ);
cifs_reconnect(server);
wake_up(&server->response_q);
return true;
--
2.20.1
next parent reply other threads:[~2019-07-26 13:59 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190726133936.11177-1-sashal@kernel.org>
2019-07-26 13:38 ` Sasha Levin [this message]
2019-07-26 13:38 ` [PATCH AUTOSEL 5.2 41/85] cifs: fix crash in cifs_dfs_do_automount Sasha Levin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190726133936.11177-31-sashal@kernel.org \
--to=sashal@kernel.org \
--cc=linux-cifs@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=lsahlber@redhat.com \
--cc=pshilov@microsoft.com \
--cc=stable@vger.kernel.org \
--cc=stfrench@microsoft.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).