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Date: Mon, 29 Oct 2012 14:34:40 -0700 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, alan@...rguk.ukuu.org.uk, Nitin Gupta <ngupta@...are.org>, Minchan Kim <minchan@...nel.org> Subject: [ 027/101] staging: zram: Fix handling of incompressible pages 3.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nitin Gupta <ngupta@...are.org> commit c8f2f0db1d0294aaf37e8a85bea9bbc4aaf5c0fe upstream. Change 130f315a (staging: zram: remove special handle of uncompressed page) introduced a bug in the handling of incompressible pages which resulted in memory allocation failure for such pages. When a page expands on compression, say from 4K to 4K+30, we were trying to do zsmalloc(pool, 4K+30). However, the maximum size which zsmalloc can allocate is PAGE_SIZE (for obvious reasons), so such allocation requests always return failure (0). For a page that has compressed size larger than the original size (this may happen with already compressed or random data), there is no point storing the compressed version as that would take more space and would also require time for decompression when needed again. So, the fix is to store any page, whose compressed size exceeds a threshold (max_zpage_size), as-it-is i.e. without compression. Memory required for storing this uncompressed page can then be requested from zsmalloc which supports PAGE_SIZE sized allocations. Lastly, the fix checks that we do not attempt to "decompress" the page which we stored in the uncompressed form -- we just memcpy() out such pages. Signed-off-by: Nitin Gupta <ngupta@...are.org> Reported-by: viechweg@...il.com Reported-by: paerley@...il.com Reported-by: wu.tommy@...il.com Acked-by: Minchan Kim <minchan@...nel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- drivers/staging/zram/zram_drv.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) --- a/drivers/staging/zram/zram_drv.c +++ b/drivers/staging/zram/zram_drv.c @@ -223,8 +223,13 @@ static int zram_bvec_read(struct zram *z cmem = zs_map_object(zram->mem_pool, zram->table[index].handle, ZS_MM_RO); - ret = lzo1x_decompress_safe(cmem, zram->table[index].size, + if (zram->table[index].size == PAGE_SIZE) { + memcpy(uncmem, cmem, PAGE_SIZE); + ret = LZO_E_OK; + } else { + ret = lzo1x_decompress_safe(cmem, zram->table[index].size, uncmem, &clen); + } if (is_partial_io(bvec)) { memcpy(user_mem + bvec->bv_offset, uncmem + offset, @@ -342,8 +347,11 @@ static int zram_bvec_write(struct zram * goto out; } - if (unlikely(clen > max_zpage_size)) + if (unlikely(clen > max_zpage_size)) { zram_stat_inc(&zram->stats.bad_compress); + src = uncmem; + clen = PAGE_SIZE; + } handle = zs_malloc(zram->mem_pool, clen); if (!handle) { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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