Re: [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial write

[Pekka Enberg <penberg@kernel.org>]

On Tue, Jan 29, 2013 at 1:21 AM, Minchan Kim <minchan@kernel.org> wrote:
> How about this?
> ------------------------- >8 -------------------------------
> 
> From 9f8756ae0b0f2819f93cb94dcd38da372843aa12 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@kernel.org>
> Date: Mon, 21 Jan 2013 13:58:52 +0900
> Subject: [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial read/write
> 
> 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_ATOMIC and GFP_NOIO.
> In read path, we called kmap_atomic so that we need GFP_ATOMIC
> while we need GFP_NOIO in write path.

The patch description makes sense now. Thanks!

On Tue, Jan 29, 2013 at 1:21 AM, Minchan Kim <minchan@kernel.org> wrote:
> We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
> some modification related to buffer allocation in case of partial IO.
> But it needs more churn and prevent merge this patch into stable
> if we should send this to stable so I'd like to keep it as simple
> as possbile. GFP_IO usage could be separate patch after we merge it.

I don't see why something like below couldn't be merged for stable.
Going for GFP_ATOMIC might seem like the simplest thing to go for but
usually bites you in the end.

			Pekka

------------------------- >8 -------------------------------

>From 936a12b423c58542628d6fd683e859f752eb3d41 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Mon, 21 Jan 2013 13:58:52 +0900
Subject: [PATCH] zram: Fix deadlock bug in partial read/write

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.

Cc: stable@vger.kernel.org
Cc: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
[ penberg@kernel.org: don't use GFP_ATOMIC ]
Signed-off-by: Pekka Enberg <penberg@kernel.org>
---
 drivers/staging/zram/zram_drv.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index f2a73bd..071e058 100644
--- 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;
-- 
1.7.11.7