[Bug 229614] ZFS lockup in zil_commit_impl

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=229614

--- Comment #19 from vi at endrift.com ---
This is the line that the _sx_xlock_hard call that's hanging is on:
https://github.com/freebsd/freebsd/blob/release/11.2.0/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zil.c#L2190
(beginning of zil_commit_writer). That means that the issuer lock is being held
by something.

Notably, the issuer lock can be held while waiting on a txg to sync in
zil_commit_waiter_timeout (or more precisely, its call to
zil_commit_writer_stall). I'm not entirely sure (since I'm unfamiliar with this
code), but I think this may be the source of the deadlock. Upon inspection,
both the quiesce and sync threads appear to be idle, and I can't find any
evidence that there's any other thread that's in that function, so I'm not sure
that's what's going on. Plus I have no idea what's going on with the
un-ptraceable process as mentioned in comment 9, which I've observed too. It
appears to be livelocked on my system (100% of one thread at all times), but I
can't inspect it at all--even kgdb can't touch it.

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