git: f1650b162d26 - stable/13 - Make sbuf_drain safe for external use

[Richard Scheffenegger]

The branch stable/13 has been updated by rscheff:

URL: https://cgit.FreeBSD.org/src/commit/?id=f1650b162d26b91b6b170f10250f46617a0bcedc

commit f1650b162d26b91b6b170f10250f46617a0bcedc
Author:     Richard Scheffenegger <rscheff at FreeBSD.org>
AuthorDate: 2021-04-02 18:11:45 +0000
Commit:     Richard Scheffenegger <rscheff at FreeBSD.org>
CommitDate: 2021-04-16 18:51:20 +0000

    Make sbuf_drain safe for external use
    
    While sbuf_drain was an internal function, two
    KASSERTS checked the sanity of it being called.
    However, an external caller may be ignorant if
    there is any data to drain, or if an error has
    already accumulated. Be nice and return immediately
    with the accumulated error.
    
    MFC after: 2 weeks
    Reviewed By: tuexen, #transport
    Sponsored by: NetApp, Inc.
    Differential Revision: https://reviews.freebsd.org/D29544
    
    (cherry picked from commit cad4fd0365a5e3235e715e072e6ee9dffaa7a3ab)
---
 sys/kern/subr_sbuf.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/sys/kern/subr_sbuf.c b/sys/kern/subr_sbuf.c
index 66822115dbcb..cdeaf690208f 100644
--- a/sys/kern/subr_sbuf.c
+++ b/sys/kern/subr_sbuf.c
@@ -388,8 +388,12 @@ sbuf_drain(struct sbuf *s)
 {
 	int len;
 
-	KASSERT(s->s_len > 0, ("Shouldn't drain empty sbuf %p", s));
-	KASSERT(s->s_error == 0, ("Called %s with error on %p", __func__, s));
+	/*
+	 * Immediately return when no work to do,
+	 * or an error has already been accumulated.
+	 */
+	if ((s->s_len == 0) || (s->s_error != 0))
+		return(s->s_error);
 
 	if (SBUF_DODRAINTOEOR(s) && s->s_rec_off == 0)
 		return (s->s_error = EDEADLK);