• Johannes Weiner's avatar
    mm: memcontrol: do not recurse in direct reclaim · 89a28483
    Johannes Weiner authored
    On 4.0, we saw a stack corruption from a page fault entering direct
    memory cgroup reclaim, calling into btrfs_releasepage(), which then
    tried to allocate an extent and recursed back into a kmem charge ad
    nauseam:
    
      [...]
      btrfs_releasepage+0x2c/0x30
      try_to_release_page+0x32/0x50
      shrink_page_list+0x6da/0x7a0
      shrink_inactive_list+0x1e5/0x510
      shrink_lruvec+0x605/0x7f0
      shrink_zone+0xee/0x320
      do_try_to_free_pages+0x174/0x440
      try_to_free_mem_cgroup_pages+0xa7/0x130
      try_charge+0x17b/0x830
      memcg_charge_kmem+0x40/0x80
      new_slab+0x2d9/0x5a0
      __slab_alloc+0x2fd/0x44f
      kmem_cache_alloc+0x193/0x1e0
      alloc_extent_state+0x21/0xc0
      __clear_extent_bit+0x2b5/0x400
      try_release_extent_mapping+0x1a3/0x220
      __btrfs_releasepage+0x31/0x70
      btrfs_releasepage+0x2c/0x30
      try_to_release_page+0x32/0x50
      shrink_page_list+0x6da/0x7a0
      shrink_inactive_list+0x1e5/0x510
      shrink_lruvec+0x605/0x7f0
      shrink_zone+0xee/0x320
      do_try_to_free_pages+0x174/0x440
      try_to_free_mem_cgroup_pages+0xa7/0x130
      try_charge+0x17b/0x830
      mem_cgroup_try_charge+0x65/0x1c0
      handle_mm_fault+0x117f/0x1510
      __do_page_fault+0x177/0x420
      do_page_fault+0xc/0x10
      page_fault+0x22/0x30
    
    On later kernels, kmem charging is opt-in rather than opt-out, and that
    particular kmem allocation in btrfs_releasepage() is no longer being
    charged and won't recurse and overrun the stack anymore.
    
    But it's not impossible for an accounted allocation to happen from the
    memcg direct reclaim context, and we needed to reproduce this crash many
    times before we even got a useful stack trace out of it.
    
    Like other direct reclaimers, mark tasks in memcg reclaim PF_MEMALLOC to
    avoid recursing into any other form of direct reclaim.  Then let
    recursive charges from PF_MEMALLOC contexts bypass the cgroup limit.
    
    Link: http://lkml.kernel.org/r/20161025141050.GA13019@cmpxchg.orgSigned-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Acked-by: default avatarMichal Hocko <mhocko@suse.com>
    Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    89a28483
vmscan.c 111 KB