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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.
This commit is contained in:
riastradh 2022-03-20 13:18:11 +00:00
parent 5798170187
commit f7b53447aa
1 changed files with 5 additions and 3 deletions
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8
sys/kern/kern_entropy.c
View File

@ -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 *ec)
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