zram: Fix deadlock bug in partial read/write

commit 7e5a5104c6af709a8d97d5f4711e7c917761d464 upstream.

Now zram allocates new page with GFP_KERNEL in zram I/O path
if IO is partial. Unfortunately, It may cause deadlock with
reclaim path like below.

write_page from fs
fs_lock
allocation(GFP_KERNEL)
reclaim
pageout
				write_page from fs
				fs_lock <-- deadlock

This patch fixes it by using GFP_NOIO.  In read path, we
reorganize code flow so that kmap_atomic is called after the
GFP_NOIO allocation.

Acked-by: Jerome Marchand <jmarchand@redhat.com>
Acked-by: Nitin Gupta <ngupta@vflare.org>
[ penberg@kernel.org: don't use GFP_ATOMIC ]
Signed-off-by: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index f2a73bd739fb94b750e66e1ee2c931e3c971a52a..071e058af1e515cf81ead68f88995c44cd27faaa 100644 (file)
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -228,11 +228,12 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
                return 0;
        }
 
-       user_mem = kmap_atomic(page);
        if (is_partial_io(bvec))
                /* Use  a temporary buffer to decompress the page */
-               uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
-       else
+               uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
+
+       user_mem = kmap_atomic(page);
+       if (!is_partial_io(bvec))
                uncmem = user_mem;
 
        if (!uncmem) {
@@ -279,7 +280,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
                 * This is a partial IO. We need to read the full page
                 * before to write the changes.
                 */
-               uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
+               uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
                if (!uncmem) {
                        pr_info("Error allocating temp memory!\n");
                        ret = -ENOMEM;