On 7/13/19 12:39 PM, David Rientjes wrote:
On Sat, 13 Jul 2019, Yang Shi wrote:
When running ltp's oom test with kmemleak enabled, the below warning was
triggerred since kernel detects __GFP_NOFAIL & ~__GFP_DIRECT_RECLAIM is
passed in:
WARNING: CPU: 105 PID: 2138 at mm/page_alloc.c:4608 __alloc_pages_nodemask+0x1c31/0x1d50
Modules linked in: loop dax_pmem dax_pmem_core
ip_tables x_tables xfs virtio_net net_failover virtio_blk failover
ata_generic virtio_pci virtio_ring virtio libata
CPU: 105 PID: 2138 Comm: oom01 Not tainted 5.2.0-next-20190710+ #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
RIP: 0010:__alloc_pages_nodemask+0x1c31/0x1d50
...
kmemleak_alloc+0x4e/0xb0
kmem_cache_alloc+0x2a7/0x3e0
? __kmalloc+0x1d6/0x470
? ___might_sleep+0x9c/0x170
? mempool_alloc+0x2b0/0x2b0
mempool_alloc_slab+0x2d/0x40
mempool_alloc+0x118/0x2b0
? __kasan_check_read+0x11/0x20
? mempool_resize+0x390/0x390
? lock_downgrade+0x3c0/0x3c0
bio_alloc_bioset+0x19d/0x350
? __swap_duplicate+0x161/0x240
? bvec_alloc+0x1b0/0x1b0
? do_raw_spin_unlock+0xa8/0x140
? _raw_spin_unlock+0x27/0x40
get_swap_bio+0x80/0x230
? __x64_sys_madvise+0x50/0x50
? end_swap_bio_read+0x310/0x310
? __kasan_check_read+0x11/0x20
? check_chain_key+0x24e/0x300
? bdev_write_page+0x55/0x130
__swap_writepage+0x5ff/0xb20
The mempool_alloc_slab() clears __GFP_DIRECT_RECLAIM, kmemleak has
__GFP_NOFAIL set all the time due to commit
d9570ee3bd1d4f20ce63485f5ef05663866fe6c0 ("kmemleak: allow to coexist
with fault injection").
It only clears __GFP_DIRECT_RECLAIM provisionally to see if the allocation
would immediately succeed before falling back to the elements in the
mempool. If that fails, and the mempool is empty, mempool_alloc()
attempts the allocation with __GFP_DIRECT_RECLAIM. So for the problem
described here, I think what we really want is this:
diff --git a/mm/mempool.c b/mm/mempool.c
--- a/mm/mempool.c
+++ b/mm/mempool.c
@@ -386,7 +386,7 @@ void *mempool_alloc(mempool_t *pool, gfp_t gfp_mask)
gfp_mask |= __GFP_NORETRY; /* don't loop in __alloc_pages */
gfp_mask |= __GFP_NOWARN; /* failures are OK */
- gfp_temp = gfp_mask & ~(__GFP_DIRECT_RECLAIM|__GFP_IO);
+ gfp_temp = gfp_mask & ~(__GFP_DIRECT_RECLAIM|__GFP_IO|__GFP_NOFAIL);
repeat_alloc:
But bio_alloc_bioset() plays with gfp_mask itself: are we sure that it
isn't the one clearing __GFP_DIRECT_RECLAIM itself before falling back to
saved_gfp?
In other words do we also want this?
diff --git a/block/bio.c b/block/bio.c
--- a/block/bio.c
+++ b/block/bio.c
@@ -462,16 +462,16 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, unsigned int nr_iovecs,
* We solve this, and guarantee forward progress, with a rescuer
* workqueue per bio_set. If we go to allocate and there are
* bios on current->bio_list, we first try the allocation
- * without __GFP_DIRECT_RECLAIM; if that fails, we punt those
- * bios we would be blocking to the rescuer workqueue before
- * we retry with the original gfp_flags.
+ * without __GFP_DIRECT_RECLAIM or __GFP_NOFAIL; if that fails,
+ * we punt those bios we would be blocking to the rescuer
+ * workqueue before we retry with the original gfp_flags.
*/
-
if (current->bio_list &&
(!bio_list_empty(¤t->bio_list[0]) ||
!bio_list_empty(¤t->bio_list[1])) &&
bs->rescue_workqueue)
- gfp_mask &= ~__GFP_DIRECT_RECLAIM;
+ gfp_mask &= ~(__GFP_DIRECT_RECLAIM |
+ __GFP_NOFAIL);
p = mempool_alloc(&bs->bio_pool, gfp_mask);
if (!p && gfp_mask != saved_gfp) {
I don't think it will make any difference by removing __GFP_NOFAIL
outside kmemleak. The problem is the commit
d9570ee3bd1d4f20ce63485f5ef05663866fe6c0 ("kmemleak: allow to coexist
with fault injection") makes __GFP_NOFAIL is set for kmemleak always in
order to turn off fault-injection for kmemleak.
As long as kmemleak is called in ~__GFP_DIRECT_RECLAIM path, the warning
might be hit.
And since kmemleak is just a debugging tool, so IMHO I don't think this
is worth fixing, so I came up with the patch to document it.
