Re: [PATCH 1/2] zram: free meta out of init_lock

Sergey Senozhatsky
2015-01-28T03:53:57Z

On (01/28/15 11:57), Minchan Kim wrote:
[..]
> > second,
> > after kick_all_cpus_sync() new RW operations will see false init_done().
> > bdev->bd_holders protects from resetting device which has read/write
> > operation ongoing on the onther CPU.
> >
> > I need to refresh on how ->bd_holders actually incremented/decremented.
> > can the following race condition take a place?
> >
> > CPU0 CPU1
> > reset_store()
> > bdev->bd_holders == false
> > zram_make_request
> > -rm- down_read(&zram->init_lock);
> > init_done(zram) == true
> > zram_reset_device() valid_io_request()
> > __zram_make_request
> > down_write(&zram->init_lock); zram_bvec_rw
> > [..]
> > set_capacity(zram->disk, 0);
> > zram->init_done = false;
> > kick_all_cpus_sync(); zram_bvec_write or zram_bvec_read()
> > zram_meta_free(zram->meta);
> > zcomp_destroy(zram->comp); zcomp_compress() or zcomp_decompress()
>
> You're absolutely right. I forgot rw path is blockable so
> kick_all_cpus_sync doesn't work for our case, unfortunately.
> So, I want to go with srcu. Do you agree? or another suggestion?

yes, I think we need to take a second look on srcu approach.

-ss