Re: [PATCH] zsmalloc: use unsigned long instead of void *

[Minchan Kim]

On 05/21/2012 11:19 PM, Seth Jennings wrote:

> On 05/20/2012 09:23 PM, Minchan Kim wrote:
> 
>> We should use unsigned long as handle instead of void * to avoid any
>> confusion. Without this, users may just treat zs_malloc return value as
>> a pointer and try to deference it.
> 
> 
> I wouldn't have agreed with you about the need for this change as people
> should understand a void * to be the address of some data with unknown
> structure.
> 
> However, I recently discussed with Dan regarding his RAMster project
> where he assumed that the void * would be an address, and as such,
> 4-byte aligned.  So he has masked two bits into the two LSBs of the
> handle for RAMster, which doesn't work with zsmalloc since the handle is
> not an address.
> 
> So really we do need to convey as explicitly as possible to the user
> that the handle is an _opaque_ value about which no assumption can be made.
> 
> Also, I wanted to test this but is doesn't apply cleanly on
> zsmalloc-main.c on v3.4 or what I have as your latest patch series.
> What is the base for this patch?


It's based on next-20120518.
I have always used linux-next tree for staging.
Greg, What's the convenient tree for you?

Maybe I will resend next spin based on v3.4 today
I hope it doesn't hurt you.

> 
>>
>> This patch passed compile test(zram, zcache and ramster) and zram is
>> tested on qemu.
>>
>> Cc: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx>
>> Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>> Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
>> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
>> ---
>>
>> Nitin, Konrad and I discussed and concluded that we should use 'unsigned long'
>> instead of 'void *'.
>> Look at the lengthy thread if you have a question.
>> http://marc.info/?l=linux-mm&m=133716653118566&w=4
>> Watch out! it has number of noises.
>>
>>  drivers/staging/zcache/zcache-main.c     |   12 ++++++------
>>  drivers/staging/zram/zram_drv.c          |   16 ++++++++--------
>>  drivers/staging/zram/zram_drv.h          |    2 +-
>>  drivers/staging/zsmalloc/zsmalloc-main.c |   24 ++++++++++++------------
>>  drivers/staging/zsmalloc/zsmalloc.h      |    8 ++++----
>>  5 files changed, 31 insertions(+), 31 deletions(-)
>>
>> diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
>> index 2734dac..4c218a7 100644
>> --- a/drivers/staging/zcache/zcache-main.c
>> +++ b/drivers/staging/zcache/zcache-main.c
>> @@ -700,7 +700,7 @@ static struct zv_hdr *zv_create(struct zs_pool *pool, uint32_t pool_id,
>>  	struct zv_hdr *zv;
>>  	u32 size = clen + sizeof(struct zv_hdr);
>>  	int chunks = (size + (CHUNK_SIZE - 1)) >> CHUNK_SHIFT;
>> -	void *handle = NULL;
>> +	unsigned long handle = 0;
>>
>>  	BUG_ON(!irqs_disabled());
>>  	BUG_ON(chunks >= NCHUNKS);
>> @@ -718,10 +718,10 @@ static struct zv_hdr *zv_create(struct zs_pool *pool, uint32_t pool_id,
>>  	memcpy((char *)zv + sizeof(struct zv_hdr), cdata, clen);
>>  	zs_unmap_object(pool, handle);
>>  out:
>> -	return handle;
>> +	return (struct zv_hdr *)handle;
> 
> 
> This is kind of weird, and somewhat defeats the point, casting it back
> to a pointer.  I know you'd have to change it all the way up the stack.
>  Just saying.


Okay.

> 
>>  }
>>
>> -static void zv_free(struct zs_pool *pool, void *handle)
>> +static void zv_free(struct zs_pool *pool, unsigned long handle)
>>  {
>>  	unsigned long flags;
>>  	struct zv_hdr *zv;
>> @@ -743,7 +743,7 @@ static void zv_free(struct zs_pool *pool, void *handle)
>>  	local_irq_restore(flags);
>>  }
>>
>> -static void zv_decompress(struct page *page, void *handle)
>> +static void zv_decompress(struct page *page, unsigned long handle)
>>  {
>>  	unsigned int clen = PAGE_SIZE;
>>  	char *to_va;
>> @@ -1247,7 +1247,7 @@ static int zcache_pampd_get_data(char *data, size_t *bufsize, bool raw,
>>  	int ret = 0;
>>
>>  	BUG_ON(is_ephemeral(pool));
>> -	zv_decompress((struct page *)(data), pampd);
>> +	zv_decompress((struct page *)(data), (unsigned long)pampd);
>>  	return ret;
>>  }
>>
>> @@ -1282,7 +1282,7 @@ static void zcache_pampd_free(void *pampd, struct tmem_pool *pool,
>>  		atomic_dec(&zcache_curr_eph_pampd_count);
>>  		BUG_ON(atomic_read(&zcache_curr_eph_pampd_count) < 0);
>>  	} else {
>> -		zv_free(cli->zspool, pampd);
>> +		zv_free(cli->zspool, (unsigned long)pampd);
>>  		atomic_dec(&zcache_curr_pers_pampd_count);
>>  		BUG_ON(atomic_read(&zcache_curr_pers_pampd_count) < 0);
>>  	}
>> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
>> index 685d612..abd69d1 100644
>> --- a/drivers/staging/zram/zram_drv.c
>> +++ b/drivers/staging/zram/zram_drv.c
>> @@ -135,7 +135,7 @@ static void zram_set_disksize(struct zram *zram, size_t totalram_bytes)
>>
>>  static void zram_free_page(struct zram *zram, size_t index)
>>  {
>> -	void *handle = zram->table[index].handle;
>> +	unsigned long handle = zram->table[index].handle;
> 
> 
> Should we incorporate the union { handle, page } idea we were working on
> earlier before doing this?  Might cut down on some the casting below.


Yes. It should be another patch and I don't care it's applied based on
this patch or reverse.
I will try it.

> 
>>
>>  	if (unlikely(!handle)) {
>>  		/*
>> @@ -150,7 +150,7 @@ static void zram_free_page(struct zram *zram, size_t index)
>>  	}
>>
>>  	if (unlikely(zram_test_flag(zram, index, ZRAM_UNCOMPRESSED))) {
>> -		__free_page(handle);
>> +		__free_page((struct page *)handle);
>>  		zram_clear_flag(zram, index, ZRAM_UNCOMPRESSED);
>>  		zram_stat_dec(&zram->stats.pages_expand);
>>  		goto out;
>> @@ -166,7 +166,7 @@ out:
>>  			zram->table[index].size);
>>  	zram_stat_dec(&zram->stats.pages_stored);
>>
>> -	zram->table[index].handle = NULL;
>> +	zram->table[index].handle = 0;
>>  	zram->table[index].size = 0;
>>  }
>>
>> @@ -189,7 +189,7 @@ static void handle_uncompressed_page(struct zram *zram, struct bio_vec *bvec,
>>  	unsigned char *user_mem, *cmem;
>>
>>  	user_mem = kmap_atomic(page);
>> -	cmem = kmap_atomic(zram->table[index].handle);
>> +	cmem = kmap_atomic((struct page *)zram->table[index].handle);
>>
>>  	memcpy(user_mem + bvec->bv_offset, cmem + offset, bvec->bv_len);
>>  	kunmap_atomic(cmem);
>> @@ -317,7 +317,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>>  	int ret;
>>  	u32 store_offset;
>>  	size_t clen;
>> -	void *handle;
>> +	unsigned long handle;
>>  	struct zobj_header *zheader;
>>  	struct page *page, *page_store;
>>  	unsigned char *user_mem, *cmem, *src, *uncmem = NULL;
>> @@ -399,7 +399,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>>  		store_offset = 0;
>>  		zram_set_flag(zram, index, ZRAM_UNCOMPRESSED);
>>  		zram_stat_inc(&zram->stats.pages_expand);
>> -		handle = page_store;
>> +		handle = (unsigned long)page_store;
>>  		src = kmap_atomic(page);
>>  		cmem = kmap_atomic(page_store);
>>  		goto memstore;
>> @@ -592,12 +592,12 @@ void __zram_reset_device(struct zram *zram)
>>
>>  	/* Free all pages that are still in this zram device */
>>  	for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
>> -		void *handle = zram->table[index].handle;
>> +		unsigned long handle = zram->table[index].handle;
>>  		if (!handle)
>>  			continue;
>>
>>  		if (unlikely(zram_test_flag(zram, index, ZRAM_UNCOMPRESSED)))
>> -			__free_page(handle);
>> +			__free_page((struct page *)handle);
>>  		else
>>  			zs_free(zram->mem_pool, handle);
>>  	}
>> diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
>> index fbe8ac9..7a7e256 100644
>> --- a/drivers/staging/zram/zram_drv.h
>> +++ b/drivers/staging/zram/zram_drv.h
>> @@ -81,7 +81,7 @@ enum zram_pageflags {
>>
>>  /* Allocated for each disk page */
>>  struct table {
>> -	void *handle;
>> +	unsigned long handle;
> 
> 
> Putting the union here, as mentioned above.
> 
>>  	u16 size;	/* object size (excluding header) */
>>  	u8 count;	/* object ref count (not yet used) */
>>  	u8 flags;
> 
> <snip>
> 
> Thanks,
> Seth
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@xxxxxxxxxx  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
> 



-- 
Kind regards,
Minchan Kim
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/