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Re: kern/52769: hang with an ffs stored in an nvme device
The following reply was made to PR kern/52769; it has been noted by GNATS.
From: mlelstv%serpens.de@localhost (Michael van Elst)
To: gnats-bugs%netbsd.org@localhost
Cc:
Subject: Re: kern/52769: hang with an ffs stored in an nvme device
Date: Sat, 2 Dec 2017 09:51:03 -0000 (UTC)
chuq%chuq.com@localhost (Chuck Silvers) writes:
>the logic in dk_start() that allows two threads to be processing the bufq
>in parallel looks like it could result in losing track of a buffer entirely.
>if both threads get EAGAIN from d_diskstart then then will both try to
>save the buffer pointer in dksc->sc_deferred, and the first one will be lost.
Two threads cannot enter d_diskstart as the queue processing is skipped
for sc_busy > 1. Instead the first thread will retry the queue (including
a possible sc_deferred entry).
--
--
Michael van Elst
Internet: mlelstv%serpens.de@localhost
"A potential Snark may lurk in every tree."
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