linux-kernel - Re: [PATCH] jbd2: get rid of superfluous __GFP

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Message-ID: <20151108050802.GB3880@thunk.org>
Date:	Sun, 8 Nov 2015 00:08:02 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	mhocko@...nel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>, john.johansen@...onical.com
Subject: Re: [PATCH] jbd2: get rid of superfluous __GFP_REPEAT

On Sat, Nov 07, 2015 at 10:22:55AM +0900, Tetsuo Handa wrote:
> All jbd2_alloc() callers seem to pass GFP_NOFS. Therefore, use of
> vmalloc() which implicitly passes GFP_KERNEL | __GFP_HIGHMEM can cause
> deadlock, can't it? This vmalloc(size) call needs to be replaced with
> __vmalloc(size, flags).

jbd2_alloc is only passed in the bh->b_size, which can't be >
PAGE_SIZE, so the code path that calls vmalloc() should never get
called.  When we conveted jbd2_alloc() to suppor sub-page size
allocations in commit d2eecb039368, there was an assumption that it
could be called with a size greater than PAGE_SIZE, but that's
certaily not true today.

					- Ted
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