Date: Sat, 22 Dec 2012 20:51:47 +1100 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Attilio Rao <attilio@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r244582 - head/sys/kern Message-ID: <20121222204409.V1410@besplex.bde.org> In-Reply-To: <201212220937.qBM9bYQK050680@svn.freebsd.org>
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On Sat, 22 Dec 2012, Attilio Rao wrote:
> Log:
> Fixup r240424: On entering KDB backends, the hijacked thread to run
> interrupt context can still be idlethread. At that point, without the
> panic condition, it can still happen that idlethread then will try to
> acquire some locks to carry on some operations.
>
> Skip the idlethread check on block/sleep lock operations when KDB is
> active.
This seems backwards to me. It is an error to go near normal locking
code when kdb is active.
> Modified: head/sys/kern/kern_lock.c
> ==============================================================================
> --- head/sys/kern/kern_lock.c Sat Dec 22 07:48:09 2012 (r244581)
> +++ head/sys/kern/kern_lock.c Sat Dec 22 09:37:34 2012 (r244582)
> @@ -35,6 +35,7 @@
> __FBSDID("$FreeBSD$");
>
> #include <sys/param.h>
> +#include <sys/kdb.h>
> #include <sys/ktr.h>
> #include <sys/lock.h>
> #include <sys/lock_profile.h>
> @@ -477,7 +478,7 @@ __lockmgr_args(struct lock *lk, u_int fl
> KASSERT((flags & LK_INTERLOCK) == 0 || ilk != NULL,
> ("%s: LK_INTERLOCK passed without valid interlock @ %s:%d",
> __func__, file, line));
> - KASSERT(!TD_IS_IDLETHREAD(curthread),
> + KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
> ("%s: idle thread %p on lockmgr %s @ %s:%d", __func__, curthread,
> lk->lock_object.lo_name, file, line));
This is backwards from:
KASSERT(kdb_active == 0);
which makes it fatal for any thread to call here.
Of course, bugs in this area are common. Last time I tried checking for
them, I only used db_printfs() in places like _mtx_lock_flags(), and had
to turn off the printfs since they occurred too often. WIthout assertions
to inhibit them, these bugs must be more common now.
Bruce
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