Date: Wed, 7 Sep 2011 11:53:24 -0700 From: mdf@FreeBSD.org To: Charlie Martin <crmartin@sgi.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Understanding panic and exit in the kernel Message-ID: <CAMBSHm98=FykYxuWKEEvwA5fZsiDiUTtbCYhGEMig_gfyOa5cg@mail.gmail.com> In-Reply-To: <4E67B323.8000602@sgi.com> References: <4E67B323.8000602@sgi.com>
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On Wed, Sep 7, 2011 at 11:08 AM, Charlie Martin <crmartin@sgi.com> wrote: > I'm still pursuing a FreeBSD bug in "7.2-PRERELEASE FreeBSD" -- and yes, we > know this is wildly out of date, but it's not feasible to upgrade right now > -- and while trying to backport a fix suggested here > http://permalink.gmane.org/gmane.os.freebsd.current/134266 I got a situation > where the panic calls in one of these two macros from sys/queue.h > > #define QMD_LIST_CHECK_NEXT(elm, field) do { \ > if (LIST_NEXT((elm), field) != NULL && \ > LIST_NEXT((elm), field)->field.le_prev != \ > &((elm)->field.le_next)) \ > panic("Bad link elm %p next->prev != elm", (elm)); \ > } while (0) > > #define QMD_LIST_CHECK_PREV(elm, field) do { \ > if (*(elm)->field.le_prev != (elm)) \ > panic("Bad link elm %p prev->next != elm", (elm)); \ > } while (0) > > print the message, but *don't* then proceed to drop to the debugger -- > instead the system hangs, with the CPU running but I had no luck getting its > attention to force it to the debugger. > > I'm not clear just what could be causing the hangup. > > For my immediate purposes, I'd be happy with any way in which I could > brutally kill the kernel and force it to the debugger, say by replacing the > panic call with a printf followed by "1/0;". But I'm a little confused by > the panic.c code -- it prints the arguments using a var_args, and then calls > "exit(1);' What file are you looking in? The kernel panic() is in sys/kern/kern_shutdown.c, not sys/boot/common/panic.c. It will optionally call kdb_enter_why() and then boot(). Do you have the debug.debugger_on_panic sysctl set to 1? Thanks, matthew > So my questions: > > (1) will my brutal method actually force what I want or am I > misunderstanding something > (2) *which* of the several implementations of "int exit(int)" or similar is > the one called in the FreeBSD kernel? > (3) and how then does exit work?
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