Commit 29b0a825 authored by Heiko Carstens's avatar Heiko Carstens Committed by Martin Schwidefsky
Browse files

s390/etr,stp: fix possible deadlock on machine check 



The first level machine check handler for etr and stp machine checks may
call queue_work() while in nmi context. This may deadlock e.g. if the
machine check happened when the interrupted context did hold a lock, that
also will be acquired by queue_work().
Therefore split etr and stp machine check handling into first and second
level handling. The second level handling will then issue the queue_work()
call in process context which avoids the potential deadlock.

Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 7cc8944e

arch/s390/include/asm/etr.h

+6 −4
Original line number Diff line number Diff line
@@ -211,8 +211,9 @@ static inline int etr_ptff(void *ptff_block, unsigned int func) 
#define ETR_PTFF_SGS	0x43	/* set gross steering rate */



/* Functions needed by the machine check handler */

void etr_switch_to_local(void);

void etr_sync_check(void);

int etr_switch_to_local(void);

int etr_sync_check(void);

void etr_queue_work(void);



/* notifier for syncs */

extern struct atomic_notifier_head s390_epoch_delta_notifier;
@@ -253,7 +254,8 @@ struct stp_sstpi { 
} __attribute__ ((packed));



/* Functions needed by the machine check handler */

void stp_sync_check(void);

void stp_island_check(void);

int stp_sync_check(void);

int stp_island_check(void);

void stp_queue_work(void);



#endif /* __S390_ETR_H */

arch/s390/kernel/nmi.c

+12 −4
Original line number Diff line number Diff line
@@ -28,6 +28,8 @@ struct mcck_struct { 
	int kill_task;

	int channel_report;

	int warning;

	unsigned int etr_queue : 1;

	unsigned int stp_queue : 1;

	unsigned long long mcck_code;

};
@@ -81,6 +83,10 @@ void s390_handle_mcck(void) 
		if (xchg(&mchchk_wng_posted, 1) == 0)

			kill_cad_pid(SIGPWR, 1);

	}

	if (mcck.etr_queue)

		etr_queue_work();

	if (mcck.stp_queue)

		stp_queue_work();

	if (mcck.kill_task) {

		local_irq_enable();

		printk(KERN_EMERG "mcck: Terminating task because of machine "
@@ -323,13 +329,15 @@ void notrace s390_do_machine_check(struct pt_regs *regs) 
	if (mci->ed && mci->ec) {

		/* External damage */

		if (S390_lowcore.external_damage_code & (1U << ED_ETR_SYNC))

			etr_sync_check();

			mcck->etr_queue |= etr_sync_check();

		if (S390_lowcore.external_damage_code & (1U << ED_ETR_SWITCH))

			etr_switch_to_local();

			mcck->etr_queue |= etr_switch_to_local();

		if (S390_lowcore.external_damage_code & (1U << ED_STP_SYNC))

			stp_sync_check();

			mcck->stp_queue |= stp_sync_check();

		if (S390_lowcore.external_damage_code & (1U << ED_STP_ISLAND))

			stp_island_check();

			mcck->stp_queue |= stp_island_check();

		if (mcck->etr_queue || mcck->stp_queue)

			set_cpu_flag(CIF_MCCK_PENDING);

	}

	if (mci->se)

		/* Storage error uncorrected */

arch/s390/kernel/time.c

+21 −10
Original line number Diff line number Diff line
@@ -542,16 +542,17 @@ arch_initcall(etr_init); 
 * Switch to local machine check. This is called when the last usable

 * ETR port goes inactive. After switch to local the clock is not in sync.

 */

void etr_switch_to_local(void)

int etr_switch_to_local(void)

{

	if (!etr_eacr.sl)

		return;

		return 0;

	disable_sync_clock(NULL);

	if (!test_and_set_bit(ETR_EVENT_SWITCH_LOCAL, &etr_events)) {

		etr_eacr.es = etr_eacr.sl = 0;

		etr_setr(&etr_eacr);

		queue_work(time_sync_wq, &etr_work);

		return 1;

	}

	return 0;

}



/*
@@ -560,16 +561,22 @@ void etr_switch_to_local(void) 
 * After a ETR sync check the clock is not in sync. The machine check

 * is broadcasted to all cpus at the same time.

 */

void etr_sync_check(void)

int etr_sync_check(void)

{

	if (!etr_eacr.es)

		return;

		return 0;

	disable_sync_clock(NULL);

	if (!test_and_set_bit(ETR_EVENT_SYNC_CHECK, &etr_events)) {

		etr_eacr.es = 0;

		etr_setr(&etr_eacr);

		queue_work(time_sync_wq, &etr_work);

		return 1;

	}

	return 0;

}



void etr_queue_work(void)

{

	queue_work(time_sync_wq, &etr_work);

}



/*
@@ -1504,10 +1511,10 @@ static void stp_timing_alert(struct stp_irq_parm *intparm) 
 * After a STP sync check the clock is not in sync. The machine check

 * is broadcasted to all cpus at the same time.

 */

void stp_sync_check(void)

int stp_sync_check(void)

{

	disable_sync_clock(NULL);

	queue_work(time_sync_wq, &stp_work);

	return 1;

}



/*
@@ -1516,12 +1523,16 @@ void stp_sync_check(void) 
 * have matching CTN ids and have a valid stratum-1 configuration

 * but the configurations do not match.

 */

void stp_island_check(void)

int stp_island_check(void)

{

	disable_sync_clock(NULL);

	queue_work(time_sync_wq, &stp_work);

	return 1;

}



void stp_queue_work(void)

{

	queue_work(time_sync_wq, &stp_work);

}



static int stp_sync_clock(void *data)

{

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