[dm-devel] dm-io: Prevent the danging point of the sync io callback function

[Mikulas Patocka]

On Fri, 27 Jun 2014, Mike Snitzer wrote:

> On Fri, Jun 27 2014 at  2:44pm -0400,
> Mikulas Patocka <mpatocka at redhat.com> wrote:
> 
> > 
> > 
> > On Fri, 27 Jun 2014, Joe Thornber wrote:
> > 
> > > On Fri, Jun 27, 2014 at 12:01:30PM +0800, Minfei Huang wrote:
> > > > The io address in callback function will become the danging point,
> > > > cause by the thread of sync io wakes up by other threads
> > > > and return to relieve the io address,
> > > 
> > > Yes, well found.  I prefer the following fix however.
> > > 
> > > - Joe
> > 
> > It seems ok.
> > 
> > The patch is too big, I think the only change that needs to be done to fix 
> > the bug is to replace "struct task_struct *sleeper;" with "struct 
> > completion *completion;", replace "if (io->sleeper) 
> > wake_up_process(io->sleeper);" with "if (io->completion) 
> > complete(io->completion);" and declare the completion in sync_io() and 
> > wait on it instead of "while (1)" loop there.
> 
> Here is the minimalist fix you suggested (I agree that splitting out a
> minimalist fix is useful):

Acked-by: Mikulas Patocka <mpatocka at redhat.com>

>  drivers/md/dm-io.c | 22 ++++++++--------------
>  1 file changed, 8 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
> index 2a20986..e60c2ea 100644
> --- a/drivers/md/dm-io.c
> +++ b/drivers/md/dm-io.c
> @@ -10,6 +10,7 @@
>  #include <linux/device-mapper.h>
>  
>  #include <linux/bio.h>
> +#include <linux/completion.h>
>  #include <linux/mempool.h>
>  #include <linux/module.h>
>  #include <linux/sched.h>
> @@ -32,7 +33,7 @@ struct dm_io_client {
>  struct io {
>  	unsigned long error_bits;
>  	atomic_t count;
> -	struct task_struct *sleeper;
> +	struct completion *wait;
>  	struct dm_io_client *client;
>  	io_notify_fn callback;
>  	void *context;
> @@ -121,8 +122,8 @@ static void dec_count(struct io *io, unsigned int region, int error)
>  			invalidate_kernel_vmap_range(io->vma_invalidate_address,
>  						     io->vma_invalidate_size);
>  
> -		if (io->sleeper)
> -			wake_up_process(io->sleeper);
> +		if (io->wait)
> +			complete(io->wait);
>  
>  		else {
>  			unsigned long r = io->error_bits;
> @@ -385,6 +386,7 @@ static int sync_io(struct dm_io_client *client, unsigned int num_regions,
>  	 */
>  	volatile char io_[sizeof(struct io) + __alignof__(struct io) - 1];
>  	struct io *io = (struct io *)PTR_ALIGN(&io_, __alignof__(struct io));
> +	DECLARE_COMPLETION_ONSTACK(wait);
>  
>  	if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
>  		WARN_ON(1);
> @@ -393,7 +395,7 @@ static int sync_io(struct dm_io_client *client, unsigned int num_regions,
>  
>  	io->error_bits = 0;
>  	atomic_set(&io->count, 1); /* see dispatch_io() */
> -	io->sleeper = current;
> +	io->wait = &wait;
>  	io->client = client;
>  
>  	io->vma_invalidate_address = dp->vma_invalidate_address;
> @@ -401,15 +403,7 @@ static int sync_io(struct dm_io_client *client, unsigned int num_regions,
>  
>  	dispatch_io(rw, num_regions, where, dp, io, 1);
>  
> -	while (1) {
> -		set_current_state(TASK_UNINTERRUPTIBLE);
> -
> -		if (!atomic_read(&io->count))
> -			break;
> -
> -		io_schedule();
> -	}
> -	set_current_state(TASK_RUNNING);
> +	wait_for_completion_io(&wait);
>  
>  	if (error_bits)
>  		*error_bits = io->error_bits;
> @@ -432,7 +426,7 @@ static int async_io(struct dm_io_client *client, unsigned int num_regions,
>  	io = mempool_alloc(client->pool, GFP_NOIO);
>  	io->error_bits = 0;
>  	atomic_set(&io->count, 1); /* see dispatch_io() */
> -	io->sleeper = NULL;
> +	io->wait = NULL;
>  	io->client = client;
>  	io->callback = fn;
>  	io->context = context;
>