bug#51345: closed (dd with conv=fsync sometimes returns when its writes are still cached)

[GNU bug Tracking System]

Your message dated Fri, 28 Jan 2022 00:05:51 -0800
with message-id <15f47a2d-1cb2-fee6-a845-487f16806325@cs.ucla.edu>
and subject line Re: bug#51345: dd with conv=fsync sometimes returns when its 
writes are still cached
has caused the debbugs.gnu.org bug report #51345,
regarding dd with conv=fsync sometimes returns when its writes are still cached
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs@gnu.org.)


-- 
51345: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=51345
GNU Bug Tracking System
Contact help-debbugs@gnu.org with problems

--- Begin Message --- Subject: dd with conv=fsync sometimes returns when its writes are still cached Date: Sat, 23 Oct 2021 08:18:49 +0000

On Knoppix 9.1 with the Linux Kernel 5.10.10-64 x86_64 and GNU Coreutils 8.32 I wanted to overwrite my USB Thumb Drive a few times with random data via "dd if=/dev/random of=/dev/sdb bs=1M conv=fsync". While it usually takes ~2+ minutes to perform this action dd returned once after less than 60 seconds which made me a bit curious. On a later attempt dd returned with this command after ~1 minute again but the LED on my USB Thumb Drive was still blinking and an immediated executed sync on the terminal blocked for ~1 minute and once it returned the LED on my USB Thumb Drive also stopped blinking.

Knoppix 9.1 was booted as a live system from a DVD and the only another persistent storage attached to it was an internal HDD which was already overwritten the same way via a past booting session.

Unfortunately Linux is not my main operating system anymore so I randomly encountered this issue on a nearly 1 year old distribution which might be slightly outdated. But the issue is pretty severe as it can lead to significant data loss so it is worth at least reporting it (and having the "bad" behavior to always call sync after dd nonetheless will probably now continue to stay for quite a while).

--- End Message ---

--- Begin Message --- Subject: Re: bug#51345: dd with conv=fsync sometimes returns when its writes are still cached Date: Fri, 28 Jan 2022 00:05:51 -0800 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 I found a bit of time to work on this and installed the attached patch, which should address the issue. Thanks for reporting it.

0001-dd-synchronize-output-after-write-errors.patch
Description: Text Data

--- End Message ---