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Date: Wed, 28 Jan 2015 12:53:54 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Jerome Marchand <jmarchan@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Nitin Gupta <ngupta@vflare.org>
Subject: Re: [PATCH 1/2] zram: free meta out of init_lock
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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