Commit 8d4a8622 authored by Breno Leitao's avatar Breno Leitao Committed by Michael Ellerman
Browse files

powerpc/xmon: Fix invocation inside lock region 



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: default avatarBreno Leitao <leitao@debian.org>
Reviewed-by: default avatarThiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 26598f28

arch/powerpc/xmon/xmon.c

+14 −4
Original line number Diff line number Diff line
@@ -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;

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