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Fix data race between zil_commit() and zil_suspend() #14514

Merged
merged 1 commit into from
Mar 1, 2023
Merged

Fix data race between zil_commit() and zil_suspend() #14514

merged 1 commit into from
Mar 1, 2023

Commits on Mar 1, 2023

  1. Fix data race between zil_commit() and zil_suspend() 

    openzfsonwindows#206 found that it is possible to trip
`VERIFY(list_is_empty(&lwb->lwb_itxs))` when a `zil_commit()` is delayed
by the scheduler long enough for a parallel `zil_suspend()` operation to
exit `zil_commit_impl()`. This is a data race. To prevent this, we
introduce a `zilog->zl_suspend_lock` rwlock to ensure that all
outstanding `zil_commit()` operations finish before `zil_suspend()`
begins and that subsequent operations fallback to `txg_wait_synced()`
after `zil_suspend()` has begun.

On `PREEMPT_RT` Linux kernels, the `rw_enter()` implementation suffers
from writer starvation. This means that a ZIL intensive system can delay
`zil_suspend()` indefinitely. This is a pre-existing problem that
affects everything that uses rw locks, so it needs to be addressed in
the SPL.  However, builds against `PREEMPT_RT` Linux kernels are
currently broken due to a GPL symbol issue (openzfs#11097), so we can safely
disregard that issue for now.

Reported-by: Arun KV <arun.kv@datacore.com>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
    @ryao
    ryao committed Mar 1, 2023
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