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SubjectRe: dm-io: Prevent the danging point of the sync io callback function


On Fri, 27 Jun 2014, Mike Snitzer wrote:

> On Fri, Jun 27 2014 at 2:44pm -0400,
> Mikulas Patocka <mpatocka@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@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;
>


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