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

[Pekka Enberg]

On Tue, Jan 29, 2013 at 1:21 AM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
> How about this?
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> 
> From 9f8756ae0b0f2819f93cb94dcd38da372843aa12 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@xxxxxxxxxx>
> 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@xxxxxxxxxx> 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

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