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Date:      Sun, 10 Jul 2016 19:54:38 -0500
From:      Karl Denninger <karl@denninger.net>
To:        freebsd-stable@freebsd.org
Subject:   Not-so stable if you take a CAM error....
Message-ID:  <2b0c454b-c1a0-4b5b-e778-bf0939e90ae1@denninger.net>
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[-- Attachment #1 --]
Got a (nasty) surprise this afternoon on my sandbox machine.

I was updating some Raspberry Pi2 machines which involved taking the sd
card out, sticking it in an adapter and plugging it into the sandbox,
then mounting the partition and using rsync.

Unfortunately one of the cards was, unknown to me, bad and returned a
write error during the update.

The machine panic'd immediately after the CAM write error popped up.

I was quite surprised by this, since (1) the SD card was (of course)
mounted as a UFS filesystem; it shows up as a CAM device, (2) the
machine itself is running off a ZFS root on a normal host-adapter and
thus there is no comingling of the buffer cache and (3) there were no
images being run from (can't, wrong architecture!) nor any system I/O
(e.g. pagefile) going to the SD card.

I certainly understand that under some circumstances (maybe even most
circumstances) taking a hard I/O error to a system device is going to
hose you and a panic() is arguably "least astonishment" when the price
of being wrong might be a corrupted system file or worse (e.g. corrupted
paged-out RSS, etc.)  But I didn't expect a panic out a failed write to
a device that is mounted and being used purely for data.

I don't have a crash dump but can almost-certainly reproduce this if
it's something that shouldn't happen and thus merits investigation.

-- 
Karl Denninger
karl@denninger.net <mailto:karl@denninger.net>
/The Market Ticker/
/[S/MIME encrypted email preferred]/

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