Re: [Xenomai-core] [PATCH] xnpipe: fix state tracking of Linux side

[Jan Kiszka <jan.kiszka@domain.hid>]

Jan Kiszka wrote:
> The state tracking of Linux tasks queue on xnpipe events was fairly
> broken. An easy way to corrupt some xnpipe_state_t object was to kill a
> Linux task blocked on opening a /dev/rtpX device (this left the state
> object queued in xnpipe_sleep, and hell broke loose on next queuing).
> 
> Another problem that popped up after reworking xnpipe queuing was a
> stalled XNPIPE_USER_CONN after receiving a signal in xnpipe_open.
> 
> The following patch addresses both issues, appears to run fine so far
> (at least the test case no longer triggers), and also cleans up some
> redundant nklock acquisitions/releases. Nevertheless, I may miss some
> corner case that might have triggered the original design. So please
> check carefully.

While fighting over a single bit elsewhere, let's not forget this open
issue: Customer asks for a solution of the hard lock-up he faced, and
/me would like to know if this fix comes with no obvious regressions.

TIA,
Jan

> ---
>  ksrc/nucleus/pipe.c |   64 +++++++++++++++++++---------------------------------
>  1 file changed, 24 insertions(+), 40 deletions(-)
> 
> Index: b/ksrc/nucleus/pipe.c
> ===================================================================
> --- a/ksrc/nucleus/pipe.c
> +++ b/ksrc/nucleus/pipe.c
> @@ -88,38 +88,39 @@ static inline void xnpipe_minor_free(int
>  
>  static inline void xnpipe_enqueue_wait(xnpipe_state_t *state, int mask)
>  {
> -	spl_t s;
> -
> -	xnlock_get_irqsave(&nklock, s);
> -
>  	if (state->wcount++ == 0)
>  		appendq(&xnpipe_sleepq, &state->slink);
>  
>  	__setbits(state->status, mask);
> +}
>  
> -	xnlock_put_irqrestore(&nklock, s);
> +static inline void xnpipe_dequeue_wait(xnpipe_state_t *state, int mask)
> +{
> +	if (testbits(state->status, mask)) {
> +		if (--state->wcount == 0)
> +			removeq(&xnpipe_sleepq, &state->slink);
> +		__clrbits(state->status, mask);
> +	}
>  }
>  
>  /* Must be entered with nklock held. */
> -#define xnpipe_wait(__state, __mask, __s, __cond)	\
> -({							\
> -	wait_queue_head_t *__waitq;			\
> -	DEFINE_WAIT(__wait);				\
> -	int __sigpending;				\
> -							\
> -	if ((__mask) & XNPIPE_USER_WREAD)		\
> -		__waitq = &(__state)->readq;		\
> -	else						\
> -		__waitq = &(__state)->syncq;		\
> -							\
> -	xnpipe_enqueue_wait(__state, __mask);		\
> -	xnlock_put_irqrestore(&nklock, __s);		\
> +#define xnpipe_wait(__state, __mask, __s, __cond)			\
> +({									\
> +	wait_queue_head_t *__waitq;					\
> +	DEFINE_WAIT(__wait);						\
> +	int __sigpending;						\
> +									\
> +	if ((__mask) & XNPIPE_USER_WREAD)				\
> +		__waitq = &(__state)->readq;				\
> +	else								\
> +		__waitq = &(__state)->syncq;				\
> +									\
> +	xnpipe_enqueue_wait(__state, __mask);				\
> +	xnlock_put_irqrestore(&nklock, __s);				\
>  									\
>  	prepare_to_wait_exclusive(__waitq, &__wait, TASK_INTERRUPTIBLE);\
>  									\
> -	if (__cond)							\
> -		xnpipe_dequeue_wait(__state, __mask);			\
> -	else								\
> +	if (!__cond)							\
>  		schedule();						\
>  									\
>  	finish_wait(__waitq, &__wait);					\
> @@ -127,25 +128,11 @@ static inline void xnpipe_enqueue_wait(x
>  									\
>  	/* Restore the interrupt state initially set by the caller. */	\
>  	xnlock_get_irqsave(&nklock, __s);				\
> +	xnpipe_dequeue_wait(__state, __mask);				\
>  									\
>  	__sigpending;							\
>  })
>  
> -static inline void xnpipe_dequeue_wait(xnpipe_state_t *state, int mask)
> -{
> -	spl_t s;
> -
> -	xnlock_get_irqsave(&nklock, s);
> -
> -	if (testbits(state->status, mask)) {
> -		if (--state->wcount == 0)
> -			removeq(&xnpipe_sleepq, &state->slink);
> -		__clrbits(state->status, mask);
> -	}
> -
> -	xnlock_put_irqrestore(&nklock, s);
> -}
> -
>  static void xnpipe_wakeup_proc(void *cookie)
>  {
>  	xnholder_t *holder, *nholder;
> @@ -168,7 +155,6 @@ static void xnpipe_wakeup_proc(void *coo
>  			   before calling wake_up_interruptible(). */
>  			if ((rbits & XNPIPE_USER_WREAD_READY) != 0) {
>  				if (waitqueue_active(&state->readq)) {
> -					xnpipe_dequeue_wait(state, XNPIPE_USER_WREAD);
>  					xnlock_put_irqrestore(&nklock, s);
>  					wake_up_interruptible(&state->readq);
>  					rbits &= ~XNPIPE_USER_WREAD_READY;
> @@ -177,7 +163,6 @@ static void xnpipe_wakeup_proc(void *coo
>  			}
>  			if ((rbits & XNPIPE_USER_WSYNC_READY) != 0) {
>  				if (waitqueue_active(&state->syncq)) {
> -					xnpipe_dequeue_wait(state, XNPIPE_USER_WSYNC);
>  					xnlock_put_irqrestore(&nklock, s);
>  					wake_up_interruptible(&state->syncq);
>  					rbits &= ~XNPIPE_USER_WSYNC_READY;
> @@ -666,8 +651,7 @@ static int xnpipe_open(struct inode *ino
>  		sigpending = xnpipe_wait(state, XNPIPE_USER_WREAD, s,
>  					 testbits(state->status, XNPIPE_KERN_CONN));
>  		if (sigpending) {
> -			if (!testbits(state->status, XNPIPE_KERN_CONN))
> -				xnpipe_cleanup_user_conn(state);
> +			xnpipe_cleanup_user_conn(state);
>  			xnlock_put_irqrestore(&nklock, s);
>  			return -ERESTARTSYS;
>  		}

-- 
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Corporate Competence Center Embedded Linux