From 8d4a862276a9c30a269d368d324fb56529e6d5fd Mon Sep 17 00:00:00 2001
From: Breno Leitao <leitao@debian.org>
Date: Thu, 8 Nov 2018 15:12:42 -0200
Subject: [PATCH] powerpc/xmon: Fix invocation inside lock region
References: bsc#1122885
Patch-mainline: v5.0-rc1
Git-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>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
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 1e718431ac1c..1f943e884e85 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;
--
2.19.2