• Qian Cai's avatar
    mm/mempool: fix a data race in mempool_free() · abe1de42
    Qian Cai authored
    mempool_t pool.curr_nr could be accessed concurrently as noticed by
    KCSAN,
    
     BUG: KCSAN: data-race in mempool_free / remove_element
    
     write to 0xffffffffa937638c of 4 bytes by task 6359 on cpu 113:
      remove_element+0x4a/0x1c0
      remove_element at mm/mempool.c:132
      mempool_alloc+0x102/0x210
      (inlined by) mempool_alloc at mm/mempool.c:399
      bio_alloc_bioset+0x106/0x2c0
      get_swap_bio+0x49/0x230
      __swap_writepage+0x680/0xc30
      swap_writepage+0x9c/0xf0
      pageout+0x33e/0xae0
      shrink_page_list+0x1f57/0x2870
      shrink_inactive_list+0x316/0x880
      shrink_lruvec+0x8dc/0x1380
      shrink_node+0x317/0xd80
      do_try_to_free_pages+0x1f7/0xa10
      try_to_free_pages+0x26c/0x5e0
      __alloc_pages_slowpath+0x458/0x1290
      <snip>
    
     read to 0xffffffffa937638c of 4 bytes by interrupt on cpu 64:
      mempool_free+0x3e/0x150
      mempool_free at mm/mempool.c:492
      bio_free+0x192/0x280
      bio_put+0x91/0xd0
      end_swap_bio_write+0x1d8/0x280
      bio_endio+0x2c2/0x5b0
      dec_pending+0x22b/0x440 [dm_mod]
      clone_endio+0xe4/0x2c0 [dm_mod]
      bio_endio+0x2c2/0x5b0
      blk_update_request+0x217/0x940
      scsi_end_request+0x6b/0x4d0
      scsi_io_completion+0xb7/0x7e0
      scsi_finish_command+0x223/0x310
      scsi_softirq_done+0x1d5/0x210
      blk_mq_complete_request+0x224/0x250
      scsi_mq_done+0xc2/0x250
      pqi_raid_io_complete+0x5a/0x70 [smartpqi]
      pqi_irq_handler+0x150/0x1410 [smartpqi]
      __handle_irq_event_percpu+0x90/0x540
      handle_irq_event_percpu+0x49/0xd0
      handle_irq_event+0x85/0xca
      handle_edge_irq+0x13f/0x3e0
      do_IRQ+0x86/0x190
      <snip>
    
    Since the write is under pool->lock but the read is done as lockless.
    Even though the commit 5b990546 ("mempool: fix and document
    synchronization and memory barrier usage") introduced the smp_wmb() and
    smp_rmb() pair to improve the situation, it is adequate to protect it
    from data races which could lead to a logic bug, so fix it by adding
    READ_ONCE() for the read.
    Signed-off-by: default avatarQian Cai <cai@lca.pw>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Cc: Marco Elver <elver@google.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Link: http://lkml.kernel.org/r/1581446384-2131-1-git-send-email-cai@lca.pwSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    abe1de42
mempool.c 15.8 KB