Module Name: src
Committed By: riastradh
Date: Sun Mar 20 13:18:12 UTC 2022
Modified Files:
src/sys/kern: kern_entropy.c
Log Message:
entropy(9): Fix another new race in entropy_account_cpu.
The consolidation xcall can preempt entropy_enter, between when it
unlocks the per-CPU state and when it calls entropy_account_cpu, with
the effect of setting ec->ec_pending=0.
Previously this was impossible because we called entropy_account_cpu
with the per-CPU state still locked, but that doesn't work now that
the global entropy lock is an adaptive lock which might sleep which
is forbidden while the per-CPU state is locked.
To generate a diff of this commit:
cvs rdiff -u -r1.45 -r1.46 src/sys/kern/kern_entropy.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_entropy.c
diff -u src/sys/kern/kern_entropy.c:1.45 src/sys/kern/kern_entropy.c:1.46
--- src/sys/kern/kern_entropy.c:1.45 Sun Mar 20 13:17:44 2022
+++ src/sys/kern/kern_entropy.c Sun Mar 20 13:18:11 2022
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_entropy.c,v 1.45 2022/03/20 13:17:44 riastradh Exp $ */
+/* $NetBSD: kern_entropy.c,v 1.46 2022/03/20 13:18:11 riastradh Exp $ */
/*-
* Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -75,7 +75,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.45 2022/03/20 13:17:44 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.46 2022/03/20 13:18:11 riastradh Exp $");
#include <sys/param.h>
#include <sys/types.h>
@@ -750,7 +750,9 @@ entropy_account_cpu(struct entropy_cpu *
mutex_enter(&E->lock);
ec0 = entropy_cpu_get(&lock);
KASSERT(ec0 == ec);
- if (E->needed != 0 && E->needed <= ec->ec_pending) {
+ if (ec->ec_pending == 0) {
+ /* Raced with consolidation xcall. Nothing to do. */
+ } else if (E->needed != 0 && E->needed <= ec->ec_pending) {
/*
* If we have not yet attained full entropy but we can
* now, do so. This way we disseminate entropy
