| From 710fa55b30256d65bb5311bdb5ac1d0662d48dbe Mon Sep 17 00:00:00 2001 |
| From: Breno Leitao <leitao@debian.org> |
| Date: Thu, 8 Nov 2018 15:12:42 -0200 |
| Subject: powerpc/xmon: Fix invocation inside lock region |
| |
| [ Upstream commit 8d4a862276a9c30a269d368d324fb56529e6d5fd ] |
| |
| 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 <leitao@debian.org> |
| Reviewed-by: Thiago Jung Bauermann <bauerman@linux.ibm.com> |
| Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| 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 4264aedc7775..dd6badc31f45 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 */ |
| } |
| @@ -3672,6 +3674,14 @@ 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; |
| -- |
| 2.19.1 |
| |
