linux-kernel - [PATCH] vmalloc: add warning in _

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Date:	Wed,  2 May 2012 13:28:09 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	kosaki.motohiro@...il.com, rientjes@...gle.com,
	Minchan Kim <minchan@...nel.org>, Neil Brown <neilb@...e.de>,
	Artem Bityutskiy <dedekind1@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	"Theodore Ts'o" <tytso@....edu>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Steven Whitehouse <swhiteho@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	James Morris <jmorris@...ei.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Sage Weil <sage@...dream.net>
Subject: [PATCH] vmalloc: add warning in __vmalloc

Now there are several places to use __vmalloc with GFP_ATOMIC,
GFP_NOIO, GFP_NOFS but unfortunately __vmalloc calls map_vm_area
which calls alloc_pages with GFP_KERNEL to allocate page tables.
It means it's possible to happen deadlock.
I don't know why it doesn't have reported until now.

Firstly, I tried passing gfp_t to lower functions to support __vmalloc
with such flags but other mm guys don't want and decided that
all of caller should be fixed.

http://marc.info/?l=linux-kernel&m=133517143616544&w=2

To begin with, let's listen other's opinion whether they can fix it
by other approach without calling __vmalloc with such flags.

So this patch adds warning in __vmalloc_node_range to detect it and
to be fixed hopely. __vmalloc_node_range isn't random chocie because
all caller which has gfp_mask of map_vm_area use it through __vmalloc_area_node.
And __vmalloc_area_node is current static function and is called by only
__vmalloc_node_range. So warning in __vmalloc_node_range would cover all
vmalloc functions which have gfp_t argument.

I Cced related maintainers.
If I miss someone, please Cced them.

* Changelog
  * Replace WARN_ON with WARN_ON_ONCE - by Andrew Morton, Nick Piggin.

Cc: Neil Brown <neilb@...e.de>
Cc: Artem Bityutskiy <dedekind1@...il.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: "Theodore Ts'o" <tytso@....edu>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Steven Whitehouse <swhiteho@...hat.com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: James Morris <jmorris@...ei.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Sage Weil <sage@...dream.net>
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 mm/vmalloc.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index c28b0b9..def5943 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1648,6 +1648,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 	void *addr;
 	unsigned long real_size = size;

+	WARN_ON_ONCE(!(gfp_mask & __GFP_WAIT) ||
+			!(gfp_mask & __GFP_IO) ||
+			!(gfp_mask & __GFP_FS));
+
 	size = PAGE_ALIGN(size);
 	if (!size || (size >> PAGE_SHIFT) > totalram_pages)
 		goto fail;
-- 
1.7.9.5

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