[src/trunk]: src/sys/dev Do not limit the number of pending requests for the ...

[hannken <hannken%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/ebae977e5bb1
branches:  trunk
changeset: 373892:ebae977e5bb1
user:      hannken <hannken%NetBSD.org@localhost>
date:      Tue Mar 14 12:55:43 2023 +0000

description:
Do not limit the number of pending requests for the worker thread.

With wedge on vnd it prevents a deadlock when requests get queued with
biodone() -> dkstart() -> vndstrategy().

Fixes PR kern/57263 "vnd locks up when using vn_rdwr"

diffstat:

 sys/dev/vnd.c |  22 ++++++++++++++--------
 1 files changed, 14 insertions(+), 8 deletions(-)

diffs (51 lines):

diff -r fef289ed1ffc -r ebae977e5bb1 sys/dev/vnd.c
--- a/sys/dev/vnd.c     Tue Mar 14 10:36:06 2023 +0000
+++ b/sys/dev/vnd.c     Tue Mar 14 12:55:43 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vnd.c,v 1.287 2022/09/04 21:56:38 mlelstv Exp $        */
+/*     $NetBSD: vnd.c,v 1.288 2023/03/14 12:55:43 hannken Exp $        */
 
 /*-
  * Copyright (c) 1996, 1997, 1998, 2008, 2020 The NetBSD Foundation, Inc.
@@ -91,7 +91,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vnd.c,v 1.287 2022/09/04 21:56:38 mlelstv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vnd.c,v 1.288 2023/03/14 12:55:43 hannken Exp $");
 
 #if defined(_KERNEL_OPT)
 #include "opt_vnd.h"
@@ -553,11 +553,18 @@
                printf("vndstrategy(%p): unit %d\n", bp, unit);
 #endif
        if ((vnd->sc_flags & VNF_USE_VN_RDWR)) {
-               KASSERT(vnd->sc_pending >= 0 &&
-                   vnd->sc_pending <= VND_MAXPENDING(vnd));
-               while (vnd->sc_pending == VND_MAXPENDING(vnd))
-                       tsleep(&vnd->sc_pending, PRIBIO, "vndpc", 0);
+               /*
+                * Limit the number of pending requests to not exhaust
+                * resources needed for I/O but always allow the worker
+                * thread to add requests, as a wedge on vnd queues
+                * requests with biodone() -> dkstart() -> vndstrategy().
+                */
+               if (curlwp != vnd->sc_kthread) {
+                       while (vnd->sc_pending >= VND_MAXPENDING(vnd))
+                               tsleep(&vnd->sc_pending, PRIBIO, "vndpc", 0);
+               }
                vnd->sc_pending++;
+               KASSERT(vnd->sc_pending > 0);
        }
        bufq_put(vnd->sc_tab, bp);
        wakeup(&vnd->sc_tab);
@@ -674,8 +681,7 @@
                        continue;
                };
                if ((vnd->sc_flags & VNF_USE_VN_RDWR)) {
-                       KASSERT(vnd->sc_pending > 0 &&
-                           vnd->sc_pending <= VND_MAXPENDING(vnd));
+                       KASSERT(vnd->sc_pending > 0);
                        if (vnd->sc_pending-- == VND_MAXPENDING(vnd))
                                wakeup(&vnd->sc_pending);
                }