Messages in this thread | | | Subject | Re: [PATCH] mm: page_alloc: document kmemleak's non-blockable __GFP_NOFAIL case | From | Yang Shi <> | Date | Sun, 14 Jul 2019 20:43:27 -0700 |
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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.
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