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Re: [dm-devel] [PATCH] multipath: fix scsi async tur checker corruption



On Wed, Dec 21, 2011 at 09:17:52AM +0100, Hannes Reinecke wrote:
> On 12/21/2011 12:01 AM, Benjamin Marzinski wrote:
> > Since the tur checker runs asynchronously in its own thread, there is nothing
> > that keeps a path from being orphaned or deleted before the tur thread has
> > finished. When this happenes the checker struct gets deleted.  However, the tur
> > thread might still we writing to that memory.  This can lead to memory
> > corruption.  This patch adds all of the necessary data to the checker context,
> > and makes the tur thread only use that. This way, if the checker is deleted
> > while the thread is still using the context, the thread will clean up the
> > context itself.
> > 
> > Signed-off-by: Benjamin Marzinski <bmarzins redhat com>
> > ---
> >  libmultipath/checkers/tur.c |   85 +++++++++++++++++++++++++++++++++-----------
> >  libmultipath/discovery.c    |    1 
> >  2 files changed, 65 insertions(+), 21 deletions(-)
> > 
> > Index: multipath-tools-111219/libmultipath/checkers/tur.c
> > ===================================================================
> > --- multipath-tools-111219.orig/libmultipath/checkers/tur.c
> > +++ multipath-tools-111219/libmultipath/checkers/tur.c
> > @@ -35,10 +35,15 @@ struct tur_checker_context {
> >  	dev_t devt;
> >  	int state;
> >  	int running;
> > -	time_t timeout;
> > +	int fd;
> > +	unsigned int timeout;
> > +	time_t time;
> >  	pthread_t thread;
> >  	pthread_mutex_t lock;
> >  	pthread_cond_t active;
> > +	pthread_spinlock_t hldr_lock;
> > +	int holders;
> > +	char message[CHECKER_MSG_LEN];
> >  };
> >  
> >  #define TUR_DEVT(c) major((c)->devt), minor((c)->devt)
> > @@ -53,28 +58,49 @@ int libcheck_init (struct checker * c)
> >  	memset(ct, 0, sizeof(struct tur_checker_context));
> >  
> >  	ct->state = PATH_UNCHECKED;
> > +	ct->fd = -1;
> > +	ct->holders = 1;
> >  	pthread_cond_init(&ct->active, NULL);
> >  	pthread_mutex_init(&ct->lock, NULL);
> > +	pthread_spin_init(&ct->hldr_lock, PTHREAD_PROCESS_PRIVATE);
> >  	c->context = ct;
> >  
> >  	return 0;
> >  }
> >  
> > +void cleanup_context(struct tur_checker_context *ct)
> > +{
> > +	pthread_mutex_destroy(&ct->lock);
> > +	pthread_cond_destroy(&ct->active);
> > +	pthread_spin_destroy(&ct->hldr_lock);
> > +	free(ct);
> > +}
> > +
> >  void libcheck_free (struct checker * c)
> >  {
> >  	if (c->context) {
> >  		struct tur_checker_context *ct = c->context;
> > +		int holders;
> > +		pthread_t thread;
> >  
> > -		pthread_mutex_destroy(&ct->lock);
> > -		pthread_cond_destroy(&ct->active);
> > -		free(c->context);
> > +		pthread_spin_lock(&ct->hldr_lock);
> > +		ct->holders--;
> > +		holders = ct->holders;
> > +		thread = ct->thread;
> > +		pthread_spin_unlock(&ct->hldr_lock);
> > +		if (holders)
> > +			pthread_cancel(thread);
> > +		else
> > +			cleanup_context(ct);
> >  		c->context = NULL;
> >  	}
> >  	return;
> >  }
> >  
> > +#define TUR_MSG(msg, fmt, args...) snprintf(msg, CHECKER_MSG_LEN, fmt, ##args);
> > +
> >  int
> > -tur_check (struct checker * c)
> > +tur_check(int fd, unsigned int timeout, char *msg)
> >  {
> >  	struct sg_io_hdr io_hdr;
> >  	unsigned char turCmdBlk[TUR_CMD_LEN] = { 0x00, 0, 0, 0, 0, 0 };
> > @@ -90,10 +116,10 @@ tur_check (struct checker * c)
> >  	io_hdr.dxfer_direction = SG_DXFER_NONE;
> >  	io_hdr.cmdp = turCmdBlk;
> >  	io_hdr.sbp = sense_buffer;
> > -	io_hdr.timeout = c->timeout;
> > +	io_hdr.timeout = timeout;
> >  	io_hdr.pack_id = 0;
> > -	if (ioctl(c->fd, SG_IO, &io_hdr) < 0) {
> > -		MSG(c, MSG_TUR_DOWN);
> > +	if (ioctl(fd, SG_IO, &io_hdr) < 0) {
> > +		TUR_MSG(msg, MSG_TUR_DOWN);
> >  		return PATH_DOWN;
> >  	}
> >  	if ((io_hdr.status & 0x7e) == 0x18) {
> > @@ -101,7 +127,7 @@ tur_check (struct checker * c)
> >  		 * SCSI-3 arrays might return
> >  		 * reservation conflict on TUR
> >  		 */
> > -		MSG(c, MSG_TUR_UP);
> > +		TUR_MSG(msg, MSG_TUR_UP);
> >  		return PATH_UP;
> >  	}
> >  	if (io_hdr.info & SG_INFO_OK_MASK) {
> > @@ -146,14 +172,14 @@ tur_check (struct checker * c)
> >  				 * LOGICAL UNIT NOT ACCESSIBLE,
> >  				 * TARGET PORT IN STANDBY STATE
> >  				 */
> > -				MSG(c, MSG_TUR_GHOST);
> > +				TUR_MSG(msg, MSG_TUR_GHOST);
> >  				return PATH_GHOST;
> >  			}
> >  		}
> > -		MSG(c, MSG_TUR_DOWN);
> > +		TUR_MSG(msg, MSG_TUR_DOWN);
> >  		return PATH_DOWN;
> >  	}
> > -	MSG(c, MSG_TUR_UP);
> > +	TUR_MSG(msg, MSG_TUR_UP);
> >  	return PATH_UP;
> >  }
> >  
> > @@ -162,18 +188,25 @@ tur_check (struct checker * c)
> >  
> >  void cleanup_func(void *data)
> >  {
> > +	int holders;
> >  	struct tur_checker_context *ct = data;
> > +	pthread_spin_lock(&ct->hldr_lock);
> > +	ct->holders--;
> > +	holders = ct->holders;
> >  	ct->thread = 0;
> > +	pthread_spin_unlock(&ct->hldr_lock);
> > +	if (!holders)
> > +		cleanup_context(ct);
> >  }
> >  
> >  void *tur_thread(void *ctx)
> >  {
> > -	struct checker *c = ctx;
> > -	struct tur_checker_context *ct = c->context;
> > +	struct tur_checker_context *ct = ctx;
> >  	int state;
> >  
> >  	condlog(3, "%d:%d: tur checker starting up", TUR_DEVT(ct));
> >  
> > +	ct->message[0] = '\0';
> >  	/* This thread can be canceled, so setup clean up */
> >  	tur_thread_cleanup_push(ct)
> >  
> > @@ -182,7 +215,7 @@ void *tur_thread(void *ctx)
> >  	ct->state = PATH_PENDING;
> >  	pthread_mutex_unlock(&ct->lock);
> >  
> > -	state = tur_check(c);
> > +	state = tur_check(ct->fd, ct->timeout, ct->message);
> >  
> >  	/* TUR checker done */
> >  	pthread_mutex_lock(&ct->lock);
> > @@ -213,7 +246,7 @@ void tur_set_async_timeout(struct checke
> >  	struct timeval now;
> >  
> >  	gettimeofday(&now, NULL);
> > -	ct->timeout = now.tv_sec + c->timeout;
> > +	ct->time = now.tv_sec + c->timeout;
> >  }
> >  
> >  int tur_check_async_timeout(struct checker *c)
> > @@ -222,7 +255,7 @@ int tur_check_async_timeout(struct check
> >  	struct timeval now;
> >  
> >  	gettimeofday(&now, NULL);
> > -	return (now.tv_sec > ct->timeout);
> > +	return (now.tv_sec > ct->time);
> >  }
> >  
> >  extern int
> > @@ -242,7 +275,7 @@ libcheck_check (struct checker * c)
> >  		ct->devt = sb.st_rdev;
> >  
> >  	if (c->sync)
> > -		return tur_check(c);
> > +		return tur_check(c->fd, c->timeout, c->message);
> >  
> >  	/*
> >  	 * Async mode
> > @@ -276,6 +309,8 @@ libcheck_check (struct checker * c)
> >  			/* TUR checker done */
> >  			ct->running = 0;
> >  			tur_status = ct->state;
> > +			strncpy(c->message, ct->message, CHECKER_MSG_LEN);
> > +			c->message[CHECKER_MSG_LEN - 1] = '\0';
> >  		}
> >  		pthread_mutex_unlock(&ct->lock);
> >  	} else {
> > @@ -284,24 +319,32 @@ libcheck_check (struct checker * c)
> >  			pthread_mutex_unlock(&ct->lock);
> >  			condlog(3, "%d:%d: tur thread not responding, "
> >  				"using sync mode", TUR_DEVT(ct));
> > -			return tur_check(c);
> > +			return tur_check(c->fd, c->timeout, c->message);
> >  		}
> >  		/* Start new TUR checker */
> >  		ct->state = PATH_UNCHECKED;
> > +		ct->fd = c->fd;
> > +		ct->timeout = c->timeout;
> > +		pthread_spin_lock(&ct->hldr_lock);
> > +		ct->holders++;
> > +		pthread_spin_unlock(&ct->hldr_lock);
> >  		tur_set_async_timeout(c);
> >  		setup_thread_attr(&attr, 32 * 1024, 1);
> > -		r = pthread_create(&ct->thread, &attr, tur_thread, c);
> > +		r = pthread_create(&ct->thread, &attr, tur_thread, ct);
> >  		if (r) {
> >  			pthread_mutex_unlock(&ct->lock);
> >  			ct->thread = 0;
> > +			ct->holders--;
> >  			condlog(3, "%d:%d: failed to start tur thread, using"
> >  				" sync mode", TUR_DEVT(ct));
> > -			return tur_check(c);
> > +			return tur_check(c->fd, c->timeout, c->message);
> >  		}
> >  		pthread_attr_destroy(&attr);
> >  		tur_timeout(&tsp);
> >  		r = pthread_cond_timedwait(&ct->active, &ct->lock, &tsp);
> >  		tur_status = ct->state;
> > +		strncpy(c->message, ct->message,CHECKER_MSG_LEN);
> > +		c->message[CHECKER_MSG_LEN -1] = '\0';
> >  		pthread_mutex_unlock(&ct->lock);
> >  		if (ct->thread &&
> >  		    (tur_status == PATH_PENDING || tur_status == PATH_UNCHECKED)) {
> > Index: multipath-tools-111219/libmultipath/discovery.c
> > ===================================================================
> > --- multipath-tools-111219.orig/libmultipath/discovery.c
> > +++ multipath-tools-111219/libmultipath/discovery.c
> > @@ -826,6 +826,7 @@ get_state (struct path * pp, int daemon)
> >  		}
> >  		checker_set_fd(c, pp->fd);
> >  		if (checker_init(c, pp->mpp?&pp->mpp->mpcontext:NULL)) {
> > +			memset(c, 0x0, sizeof(struct checker));
> >  			condlog(3, "%s: checker init failed", pp->dev);
> >  			return PATH_UNCHECKED;
> >  		}
> > 
> Hmm. Why do we need ->holders here?
> In theory we can have only two states; async thread running or no
> thread running. I really cannot imagine a scenario where ->holders
> would be > 1.

Holders will be greater than 1 whenever the thread is running (It's
initialized to 1 in libcheck_init).  There are two holders of the
checker context. One is the thread and one is the checker structure
itself.  The checker context is created when the path first gets a
checker, and usually lasts until the path puts the checker when it is
getting either orphaned or removed.  In the async tur checker case, we
need it to last until both the the checker structure has been freed, and
the thread has finished running. Unless we wanted to do something
different in the tur code where it creates a new checker context each
time it fires off the thread, we only want to free the context when both
of these holders are gone. And since the path can be removed of orphaned
at any time with respect to the thread, we need some sort of lock to
make sure they both aren't decrementing holders at the same time,
meaning nobody would clean up the context.

Just to spell out the possible cases:

If the path's checker is freed, but the thread is still running, we
can't remove the checker context, since the thread is still using it.
This is the case that I saw causing memory corruption.

If the thread gets finished, but the path's checker is still there, we
can't remove the checker context, because the checker is still using it.
This is the standard case.  The thread usually finishes between path
checker calls, and the result needs to get pulled from the context.

Only when both of these are done can the context get freed.

-Ben

> Or, to stress the point a bit more, any scenario where holders > 1
> would most definitely be a bug, as this would indicate that an async
> tur thread is running, but we somehow failed to notice this, and
> started a new one. Which means we end with two threads doing exactly
> the same thing. And which was _exactly_ what we want to avoid with
> at startup.
> So I guess we can do away with ->holders.
> And once ->holders is gone, I doubt it'll make any sense to retain
> the spinlock, as we then just have ->thread to worry about.
> And this doesn't need to be spinlock protected, as we take care to
> synchronize during startup. And during shutdown we simply don't
> care, as pthread_cancel() will return an error if the thread is
> already done for.
> 
> Cheers,
> 
> Hannes
> -- 
> Dr. Hannes Reinecke		      zSeries & Storage
> hare suse de			      +49 911 74053 688
> SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
> GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
> 
> --
> dm-devel mailing list
> dm-devel redhat com
> https://www.redhat.com/mailman/listinfo/dm-devel


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