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powerpc/xmon: Fix invocation inside lock region

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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>
This commit is contained in:
Breno Leitao 2018-11-08 15:12:42 -02:00 committed by Michael Ellerman
parent 26598f2856
commit 8d4a862276
1 changed files with 14 additions and 4 deletions
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18
arch/powerpc/xmon/xmon.c
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@ -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;