1. 27 Apr, 2022 1 commit
    • Tejun Heo's avatar
      iocost: don't reset the inuse weight of under-weighted debtors · 8c936f9e
      Tejun Heo authored
      When an iocg is in debt, its inuse weight is owned by debt handling and
      should stay at 1. This invariant was broken when determining the amount of
      surpluses at the beginning of donation calculation - when an iocg's
      hierarchical weight is too low, the iocg is excluded from donation
      calculation and its inuse is reset to its active regardless of its
      indebtedness, triggering warnings like the following:
      
       WARNING: CPU: 5 PID: 0 at block/blk-iocost.c:1416 iocg_kick_waitq+0x392/0x3a0
       ...
       RIP: 0010:iocg_kick_waitq+0x392/0x3a0
       Code: 00 00 be ff ff ff ff 48 89 4d a8 e8 98 b2 70 00 48 8b 4d a8 85 c0 0f 85 4a fe ff ff 0f 0b e9 43 fe ff ff 0f 0b e9 4d fe ff ff <0f> 0b e9 50 fe ff ff e8 a2 ae 70 00 66 90 0f 1f 44 00 00 55 48 89
       RSP: 0018:ffffc90000200d08 EFLAGS: 00010016
       ...
        <IRQ>
        ioc_timer_fn+0x2e0/0x1470
        call_timer_fn+0xa1/0x2c0
       ...
      
      As this happens only when an iocg's hierarchical weight is negligible, its
      impact likely is limited to triggering the warnings. Fix it by skipping
      resetting inuse of under-weighted debtors.
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Reported-by: default avatarRik van Riel <riel@surriel.com>
      Fixes: c421a3eb ("blk-iocost: revamp debt handling")
      Cc: stable@vger.kernel.org # v5.10+
      Link: https://lore.kernel.org/r/YmjODd4aif9BzFuO@slm.duckdns.orgSigned-off-by: default avatarJens Axboe <axboe@kernel.dk>
      8c936f9e
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