1. 09 Dec, 2017 2 commits
    • Rui Hua's avatar
      bcache: recover data from backing when data is clean · 3f7477e6
      Rui Hua authored
      commit e393aa24 upstream.
      
      When we send a read request and hit the clean data in cache device, there
      is a situation called cache read race in bcache(see the commit in the tail
      of cache_look_up(), the following explaination just copy from there):
      The bucket we're reading from might be reused while our bio is in flight,
      and we could then end up reading the wrong data. We guard against this
      by checking (in bch_cache_read_endio()) if the pointer is stale again;
      if so, we treat it as an error (s->iop.error = -EINTR) and reread from
      the backing device (but we don't pass that error up anywhere)
      
      It should be noted that cache read race happened under normal
      circumstances, not the circumstance when SSD failed, it was counted
      and shown in  /sys/fs/bcache/XXX/internal/cache_read_races.
      
      Without this patch, when we use writeback mode, we will never reread from
      the backing device when cache read race happened, until the whole cache
      device is clean, because the condition
      (s->recoverable && (dc && !atomic_read(&dc->has_dirty))) is false in
      cached_dev_read_error(). In this situation, the s->iop.error(= -EINTR)
      will be passed up, at last, user will receive -EINTR when it's bio end,
      this is not suitable, and wield to up-application.
      
      In this patch, we use s->read_dirty_data to judge whether the read
      request hit dirty data in cache device, it is safe to reread data from
      the backing device when the read request hit clean data. This can not
      only handle cache read race, but also recover data when failed read
      request from cache device.
      
      [edited by mlyle to fix up whitespace, commit log title, comment
      spelling]
      
      Fixes: d59b2379 ("bcache: only permit to recovery read error when cache device is clean")
      Signed-off-by: default avatarHua Rui <huarui.dev@gmail.com>
      Reviewed-by: default avatarMichael Lyle <mlyle@lyle.org>
      Reviewed-by: default avatarColy Li <colyli@suse.de>
      Signed-off-by: default avatarMichael Lyle <mlyle@lyle.org>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      3f7477e6
    • Coly Li's avatar
      bcache: only permit to recovery read error when cache device is clean · f80f34d8
      Coly Li authored
      commit d59b2379 upstream.
      
      When bcache does read I/Os, for example in writeback or writethrough mode,
      if a read request on cache device is failed, bcache will try to recovery
      the request by reading from cached device. If the data on cached device is
      not synced with cache device, then requester will get a stale data.
      
      For critical storage system like database, providing stale data from
      recovery may result an application level data corruption, which is
      unacceptible.
      
      With this patch, for a failed read request in writeback or writethrough
      mode, recovery a recoverable read request only happens when cache device
      is clean. That is to say, all data on cached device is up to update.
      
      For other cache modes in bcache, read request will never hit
      cached_dev_read_error(), they don't need this patch.
      
      Please note, because cache mode can be switched arbitrarily in run time, a
      writethrough mode might be switched from a writeback mode. Therefore
      checking dc->has_data in writethrough mode still makes sense.
      
      Changelog:
      V4: Fix parens error pointed by Michael Lyle.
      v3: By response from Kent Oversteet, he thinks recovering stale data is a
          bug to fix, and option to permit it is unnecessary. So this version
          the sysfs file is removed.
      v2: rename sysfs entry from allow_stale_data_on_failure  to
          allow_stale_data_on_failure, and fix the confusing commit log.
      v1: initial patch posted.
      
      [small change to patch comment spelling by mlyle]
      Signed-off-by: default avatarColy Li <colyli@suse.de>
      Signed-off-by: default avatarMichael Lyle <mlyle@lyle.org>
      Reported-by: default avatarArne Wolf <awolf@lenovo.com>
      Reviewed-by: default avatarMichael Lyle <mlyle@lyle.org>
      Cc: Kent Overstreet <kent.overstreet@gmail.com>
      Cc: Nix <nix@esperi.org.uk>
      Cc: Kai Krakow <hurikhan77@gmail.com>
      Cc: Eric Wheeler <bcache@lists.ewheeler.net>
      Cc: Junhui Tang <tang.junhui@zte.com.cn>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      f80f34d8
  2. 05 Dec, 2017 28 commits
  3. 30 Nov, 2017 10 commits