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Subject[RFC] mm: kmemleak: replace __GFP_NOFAIL to GFP_NOWAIT in gfp_kmemleak_mask
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__GFP_NORETRY and  __GFP_NOFAIL are combined in gfp_kmemleak_mask now.
But it's a wrong combination. As __GFP_NOFAIL is blockable, but
__GFP_NORETY is not blockable, make it self-contradiction.

__GFP_NOFAIL means 'The VM implementation _must_ retry infinitely'. But
it's not the real intention, as kmemleak allow alloc failure happen in
memory pressure, in that case kmemleak just disables itself.

commit 9a67f6488eca ("mm: consolidate GFP_NOFAIL checks in the allocator
slowpath") documented that what user wants here should use GFP_NOWAIT, and
the WARN in __alloc_pages_slowpath caught this weird usage.

<snip>
WARNING: CPU: 3 PID: 64 at mm/page_alloc.c:4261 __alloc_pages_slowpath+0x1cc3/0x2780
CPU: 3 PID: 64 Comm: kswapd1 Not tainted 4.17.0-rc1.syzcaller+ #12
Hardware name: Red Hat KVM, BIOS 0.0.0 02/06/2015
RIP: 0010:__alloc_pages_slowpath+0x1cc3/0x2780
RSP: 0000:ffff88002fa5e6c8 EFLAGS: 00010046
RAX: 0000000000000000 RBX: 0000000000010000 RCX: 1ffff10005f4bcb6
RDX: 1ffff10007da3f46 RSI: 0000000000000000 RDI: ffff88003ed1fa38
RBP: 0000000001000000 R08: 0000000000000040 R09: 0000000000000030
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
kmemleak: Kernel memory leak detector disabled
R13: ffff88002fa5ea68 R14: dffffc0000000000 R15: ffff88002fa5ea68
FS: 0000000000000000(0000) GS:ffff88003e900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5db91c6640 CR3: 0000000004014000 CR4: 00000000001406e0
Call Trace:
__alloc_pages_nodemask+0x5ce/0x7c0
alloc_pages_current+0xb6/0x230
new_slab+0x29d/0x9f0
___slab_alloc+0x4e5/0xa90
__slab_alloc.isra.37+0x92/0x120
kmem_cache_alloc+0x35f/0x580
create_object+0xa6/0xaf0
kmem_cache_alloc+0x20a/0x580
mempool_alloc+0x13a/0x350
bio_alloc_bioset+0x3ef/0x6e0
get_swap_bio+0x125/0x490
__swap_writepage+0x7be/0x11f0
swap_writepage+0x46/0xb0
pageout.isra.33+0x435/0xe70
? trace_event_raw_event_mm_shrink_slab_start+0x4d0/0x4d0
? page_mapped+0x165/0x3f0
shrink_page_list+0x1ded/0x3960
shrink_inactive_list+0x737/0x14b0
shrink_node_memcg+0xa9f/0x1ef0
shrink_node+0x376/0x15f0
balance_pgdat+0x2c9/0x970
kswapd+0x537/0xfe0
kthread+0x387/0x510
<snip>

Replace the __GFP_NOFAIL with GFP_NOWAIT in gfp_kmemleak_mask, __GFP_NORETRY
and GFP_NOWAIT are in the gfp_kmemleak_mask. So kmemleak object allocaion
is no blockable and no reclaim, making kmemleak less disruptive to user
processes in pressure.

Signed-off-by: Chunyu Hu <chuhu@redhat.com>
CC: Michal Hocko <mhocko@suse.com>
---
mm/kmemleak.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 9a085d5..4ea07e4 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -126,7 +126,7 @@
/* GFP bitmask for kmemleak internal allocations */
#define gfp_kmemleak_mask(gfp) (((gfp) & (GFP_KERNEL | GFP_ATOMIC)) | \
__GFP_NORETRY | __GFP_NOMEMALLOC | \
- __GFP_NOWARN | __GFP_NOFAIL)
+ __GFP_NOWARN | GFP_NOWAIT)

/* scanning area inside a memory block */
struct kmemleak_scan_area {
--
1.8.3.1
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