git: 9f3835013032 - stable/13 - tcp: Shouldn't drain empty sbuf

[Richard Scheffenegger]

The branch stable/13 has been updated by rscheff:

URL: https://cgit.FreeBSD.org/src/commit/?id=9f38350130322d0fbfaa250946f0841f50d743b5

commit 9f38350130322d0fbfaa250946f0841f50d743b5
Author:     Richard Scheffenegger <rscheff at FreeBSD.org>
AuthorDate: 2021-04-01 15:18:04 +0000
Commit:     Richard Scheffenegger <rscheff at FreeBSD.org>
CommitDate: 2021-04-16 19:53:36 +0000

    tcp: Shouldn't drain empty sbuf
    
    MFC after: 2 weeks
    Reviewed By: tuexen, #transport
    Sponsored by: NetApp, Inc.
    Differential Revision: https://reviews.freebsd.org/D29524
    
    (cherry picked from commit 9aef4e7c2bd4371e526e4e3feb26064d361ad8ce)
---
 sys/netinet/tcp_hostcache.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/sys/netinet/tcp_hostcache.c b/sys/netinet/tcp_hostcache.c
index 36439e90a611..a8c4b2b178cd 100644
--- a/sys/netinet/tcp_hostcache.c
+++ b/sys/netinet/tcp_hostcache.c
@@ -644,6 +644,7 @@ sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS)
 	const int linesize = 128;
 	struct sbuf sb;
 	int i, error, len;
+	bool do_drain = false;
 	struct hc_metrics *hc_entry;
 	char ip4buf[INET_ADDRSTRLEN];
 #ifdef INET6
@@ -701,9 +702,16 @@ sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS)
 			    hc_entry->rmx_hits,
 			    hc_entry->rmx_updates,
 			    hc_entry->rmx_expire);
+			do_drain = true;
 		}
 		THC_UNLOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
-		sbuf_drain(&sb);
+		/* Need to track if sbuf has data, to avoid
+		 * a KASSERT when calling sbuf_drain.
+		 */
+		if (do_drain) {
+			sbuf_drain(&sb);
+			do_drain = false;
+		}
 	}
 #undef msec
 	error = sbuf_finish(&sb);
@@ -769,7 +777,7 @@ tcp_hc_purge_internal(int all)
 			KASSERT(V_tcp_hostcache.hashbase[i].hch_length > 0 &&
 				V_tcp_hostcache.hashbase[i].hch_length <=
 				V_tcp_hostcache.bucket_limit,
-				("tcp_hostcache: bucket langth out of range at %u: %u",
+				("tcp_hostcache: bucket length out of range at %u: %u",
 				i, V_tcp_hostcache.hashbase[i].hch_length));
 			if (all || hc_entry->rmx_expire <= 0) {
 				TAILQ_REMOVE(&V_tcp_hostcache.hashbase[i].hch_bucket,