[PATCH] vmalloc: add warning in __vmalloc

[Minchan Kim]

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@xxxxxxx>
Cc: Artem Bityutskiy <dedekind1@xxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Steven Whitehouse <swhiteho@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Sage Weil <sage@xxxxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 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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