From: Breno Leitao leitao@debian.org
[ 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 a5938fadd031..f752f771f29d 100644 --- a/arch/powerpc/xmon/xmon.c +++ b/arch/powerpc/xmon/xmon.c @@ -78,6 +78,9 @@ 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);
@@ -357,7 +360,6 @@ 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 @@ -366,11 +368,11 @@ 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 */ } @@ -3472,6 +3474,14 @@ 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;