Breno Leitao <lei...@debian.org> writes:
> Currently xmon needs to get devtree_lock (through rtas_token()) during its
> invocation (at crash time). If there is a crash while devtree_lock is being
> held, then xmon tries to get the lock but spins forever and never get into
> the interactive debugger, as in the following case:
>
> int *ptr = NULL;
> raw_spin_lock_irqsave(&devtree_lock, flags);
> *ptr = 0xdeadbeef;
>
> This patch avoids calling rtas_token(), thus trying to get the same lock,
> at crash time. This new mechanism proposes getting the token at
> initialization time (xmon_init()) and just consuming it at crash time.
>
> This would allow xmon to be possible invoked independent of devtree_lock
> being held or not.
>
> Signed-off-by: Breno Leitao <lei...@debian.org>
I'm not familiar with xmon code but I was curious, and for what it's
worth:
Reviewed-by: Thiago Jung Bauermann <bauer...@linux.ibm.com>
> ---
> arch/powerpc/xmon/xmon.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 36b8dc47a3c3..b566203d09c5 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -75,6 +75,9 @@ static int xmon_gate;
> #define xmon_owner 0
> #endif /* CONFIG_SMP */
>
> +#ifdef CONFIG_PPC_PSERIES
> +static int set_indicator_token = RTAS_UNKNOWN_SERVICE;
> +#endif
> static unsigned long in_xmon __read_mostly = 0;
> static int xmon_on = IS_ENABLED(CONFIG_XMON_DEFAULT);
>
> @@ -358,7 +361,6 @@ static inline void disable_surveillance(void)
> #ifdef CONFIG_PPC_PSERIES
> /* Since this can't be a module, args should end up below 4GB. */
> static struct rtas_args args;
> - int token;
>
> /*
> * At this point we have got all the cpus we can into
> @@ -367,11 +369,11 @@ static inline void disable_surveillance(void)
> * If we did try to take rtas.lock there would be a
> * real possibility of deadlock.
> */
> - token = rtas_token("set-indicator");
> - if (token == RTAS_UNKNOWN_SERVICE)
> + if (set_indicator_token == RTAS_UNKNOWN_SERVICE)
> return;
>
> - rtas_call_unlocked(&args, token, 3, 1, NULL, SURVEILLANCE_TOKEN, 0, 0);
> + rtas_call_unlocked(&args, set_indicator_token, 3, 1, NULL,
> + SURVEILLANCE_TOKEN, 0, 0);
>
> #endif /* CONFIG_PPC_PSERIES */
> }
> @@ -3688,6 +3690,14 @@ static void xmon_init(int enable)
> __debugger_iabr_match = xmon_iabr_match;
> __debugger_break_match = xmon_break_match;
> __debugger_fault_handler = xmon_fault_handler;
> +
> +#ifdef CONFIG_PPC_PSERIES
> + /*
> + * Get the token here to avoid trying to get a lock
> + * during the crash, causing a deadlock.
> + */
> + set_indicator_token = rtas_token("set-indicator");
> +#endif
> } else {
> __debugger = NULL;
> __debugger_ipi = NULL;
--
Thiago Jung Bauermann
IBM Linux Technology Center
