Re: [PATCH] Revert "kmemleak: allow to coexist with fault injection"

[Qian Cai]

On Wed, 2019-07-17 at 01:50 +0800, 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
> ...
> Âkmemleak_alloc+0x4e/0xb0
> Âkmem_cache_alloc+0x2a7/0x3e0
> Â? __kmalloc+0x1d6/0x470
> Â? ___might_sleep+0x9c/0x170
> Â? mempool_alloc+0x2b0/0x2b0
> Âmempool_alloc_slab+0x2d/0x40
> Âmempool_alloc+0x118/0x2b0
> Â? __kasan_check_read+0x11/0x20
> Â? mempool_resize+0x390/0x390
> Â? lock_downgrade+0x3c0/0x3c0
> Âbio_alloc_bioset+0x19d/0x350
> Â? __swap_duplicate+0x161/0x240
> Â? bvec_alloc+0x1b0/0x1b0
> Â? do_raw_spin_unlock+0xa8/0x140
> Â? _raw_spin_unlock+0x27/0x40
> Âget_swap_bio+0x80/0x230
> Â? __x64_sys_madvise+0x50/0x50
> Â? end_swap_bio_read+0x310/0x310
> Â? __kasan_check_read+0x11/0x20
> Â? check_chain_key+0x24e/0x300
> Â? bdev_write_page+0x55/0x130
> Â__swap_writepage+0x5ff/0xb20
> 
> The mempool_alloc_slab() clears __GFP_DIRECT_RECLAIM, however kmemleak has
> __GFP_NOFAIL set all the time due to commit
> d9570ee3bd1d4f20ce63485f5ef05663866fe6c0 ("kmemleak: allow to coexist
> with fault injection").ÂÂBut, it doesn't make any sense to have
> __GFP_NOFAIL and ~__GFP_DIRECT_RECLAIM specified at the same time.
> 
> According to the discussion on the mailing list, the commit should be
> reverted for short term solution.ÂÂCatalin Marinas would follow up with a
> better
> solution for longer term.
> 
> The failure rate of kmemleak metadata allocation may increase in some
> circumstances, but this should be expected side effect.

As mentioned in anther thread, the situation for kmemleak under memory pressure
has already been unhealthy. I don't feel comfortable to make it even worse by
reverting this commit alone. This could potentially make kmemleak kill itself
easier and miss some more real memory leak later.

To make it really a short-term solution before the reverting, I think someone
needs to follow up with the mempool solution with tunable pool size mentioned
in,

https://lore.kernel.org/linux-mm/20190328145917.GC10283@xxxxxxxxxxxxxxxxxxxx/

I personally not very confident that Catalin will find some time soon to
implement embedding kmemleak metadata into the slab. Even he or someone does
eventually, it probably need quite some time to test and edge out many of corner
cases that kmemleak could have by its natural.

> 
> Suggested-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Qian Cai <cai@xxxxxx>
> Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> ---
> Âmm/kmemleak.c | 2 +-
> Â1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index 9dd581d..884a5e3 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -114,7 +114,7 @@
> Â/* GFP bitmask for kmemleak internal allocations */
> Â#define gfp_kmemleak_mask(gfp)	(((gfp) & (GFP_KERNEL | GFP_ATOMIC)) |
> \
> Â				Â__GFP_NORETRY | __GFP_NOMEMALLOC | \
> -				Â__GFP_NOWARN | __GFP_NOFAIL)
> +				Â__GFP_NOWARN)
> Â
> Â/* scanning area inside a memory block */
> Âstruct kmemleak_scan_area {