diff options
| author | pho <pho@NetBSD.org> | 2023-06-27 01:15:22 +0000 |
|---|---|---|
| committer | pho <pho@NetBSD.org> | 2023-06-27 01:15:22 +0000 |
| commit | 34e8508d21d6b11b3f08cd6d621bda3ad80a66f8 (patch) | |
| tree | 8374c220037f865c0c35368b958530a012c3ba29 /sys | |
| parent | 8e39f005c1a069e0fad7ac39c87bfbfdb9c896bf (diff) | |
callout(9): Fix panic() in callout_destroy() (kern/57226)
The culprit was callout_halt(). "(c->c_flags & CALLOUT_FIRED) != 0" wasn't
the correct way to check if a callout is running. It failed to wait for a
running callout to finish in the following scenario:
1. cpu0 initializes a callout and schedules it.
2. cpu0 invokes callout_softlock() and fires the callout, setting the flag
CALLOUT_FIRED.
3. The callout invokes callout_schedule() to re-schedule itself.
4. callout_schedule_locked() clears the flag CALLOUT_FIRED, and releases
the lock.
5. Before the lock is re-acquired by callout_softlock(), cpu1 decides to
destroy the callout. It first invokes callout_halt() to make sure the
callout finishes running.
6. But since CALLOUT_FIRED has been cleared, callout_halt() thinks it's not
running and therefore returns without invoking callout_wait().
7. cpu1 proceeds to invoke callout_destroy() while it's still running on
cpu0. callout_destroy() detects that and panics.
Diffstat (limited to 'sys')
| -rw-r--r-- | sys/kern/kern_timeout.c | 14 |
1 files changed, 7 insertions, 7 deletions
diff --git a/sys/kern/kern_timeout.c b/sys/kern/kern_timeout.c index 3f3338a6787..5a7912c3d08 100644 --- a/sys/kern/kern_timeout.c +++ b/sys/kern/kern_timeout.c @@ -1,4 +1,4 @@ -/* $NetBSD: kern_timeout.c,v 1.73 2022/10/29 00:19:21 riastradh Exp $ */ +/* $NetBSD: kern_timeout.c,v 1.74 2023/06/27 01:15:22 pho Exp $ */ /*- * Copyright (c) 2003, 2006, 2007, 2008, 2009, 2019 The NetBSD Foundation, Inc. @@ -59,7 +59,7 @@ */ #include <sys/cdefs.h> -__KERNEL_RCSID(0, "$NetBSD: kern_timeout.c,v 1.73 2022/10/29 00:19:21 riastradh Exp $"); +__KERNEL_RCSID(0, "$NetBSD: kern_timeout.c,v 1.74 2023/06/27 01:15:22 pho Exp $"); /* * Timeouts are kept in a hierarchical timing wheel. The c_time is the @@ -542,7 +542,7 @@ callout_halt(callout_t *cs, void *interlock) { callout_impl_t *c = (callout_impl_t *)cs; kmutex_t *lock; - int flags; + struct callout_cpu *cc; KASSERT(c->c_magic == CALLOUT_MAGIC); KASSERT(!cpu_intr_p()); @@ -552,11 +552,11 @@ callout_halt(callout_t *cs, void *interlock) lock = callout_lock(c); SDT_PROBE4(sdt, kernel, callout, halt, c, c->c_func, c->c_arg, c->c_flags); - flags = c->c_flags; - if ((flags & CALLOUT_PENDING) != 0) + if ((c->c_flags & CALLOUT_PENDING) != 0) CIRCQ_REMOVE(&c->c_list); - c->c_flags = flags & ~(CALLOUT_PENDING|CALLOUT_FIRED); - if (__predict_false(flags & CALLOUT_FIRED)) { + c->c_flags &= ~(CALLOUT_PENDING|CALLOUT_FIRED); + cc = c->c_cpu; + if (__predict_false(cc->cc_active == c && cc->cc_lwp != curlwp)) { callout_wait(c, interlock, lock); return true; } |
