Hi Fabio,
> [1] But now when I try to obtain an IP using dhcp without specifying any
> timeout,
> it dumps lots of "Lowered timeout to match user request" messages.
> Is that expected?
>
> https://pastebin.ubuntu.com/p/5Tpc5Rwdkq/
No, this is a regression without `-t`, and has to be fixed before SRU.
...
Without `-t`, loop_timeout == -1, which makes the new check pass/true.
(because `start` ~= `now` (seconds range), even for the theoretically
lowest possible value of `timeout` (zero; note it's not loop_timeout).
We need a gating `loop_timeout >= 0` check, as used in the inner loop.
- if (now.tv_sec + timeout > start + loop_timeout) {
+ if (loop_timeout >= 0 && now.tv_sec + timeout > start +
loop_timeout) {
...
While checking the code in detail, I was a bit concerned that,
in the first pass, the `prev = now` assignment in the inner loop
now takes the newly used `now` (this patch), not the one from before
the while loop.
However, that shouldn't matter much, as it's only used for time/delta
reporting (disabled in non-debug build; but just for correctness) and
even so, for the first pass the time difference between the first/start
`now` and that assignment in the new check doesn't seem to be significant.
...
That one line change worked fine in a quick test here.
Could you test that, by, I guess (sorry, I have to EOD):
... unpacking the source package from the unapproved queue
(dpkg-source -x *.dsc && cd klibc-*),
create a new patch with `quilt new ipconfig-timeout-fix-fix.patch`,
add file with `quilt add usr/kinit/ipconfig/main.c`,
change that file,
update patch with `quilt refresh`,
update changelog `DEB_EMAIL="Your Name <y...@na.me>" TZ=UTC dch -l+test
'd/p/ipcfg-tmo-f-f.patch: Test fix'`
sudo apt build-dep -y klibc
dpkg-buildpackage -us -uc
Thanks!
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https://bugs.launchpad.net/bugs/1947099
Title:
ipconfig does not honour user-requested timeouts in some cases
Status in klibc package in Ubuntu:
New
Status in klibc source package in Bionic:
Incomplete
Bug description:
[Impact]
In some cases, ipconfig can take a longer time than the user-specified
timeouts, causing unexpected delays.
[Test Plan]
Any situation where ipconfig encounters an error sending the DHCP packet, it
will automatically set a delay of 10 seconds, which could be longer than the
user-specified timeout. It can be reproduced by creating a dummy interface and
attempting to run ipconfig on it with a timeout value of less than 10:
# ip link add eth1 type dummy
# date; /usr/lib/klibc/bin/ipconfig -t 2 eth1; date
Thu Nov 18 04:46:13 EST 2021
IP-Config: eth1 hardware address ae:e0:f5:9d:7e:00 mtu 1500 DHCP RARP
IP-Config: no response after 2 secs - giving up
Thu Nov 18 04:46:23 EST 2021
^ Notice above, ipconfig thinks that it waited 2 seconds, but the
timestamps show an actual delay of 10 seconds.
[Where problems could occur]
Please see reproduction steps above. We are seeing this in production too
(see comment #2).
[Other Info]
A patch to fix the issue is being proposed here. It is a safe fix - it only
checks before going into sleep that the timeout never exceeds the
user-requested value.
[Original Description]
In some cases, ipconfig can take longer than the user-specified
timeouts, causing unexpected delays.
in main.c, in function loop(), the process can go into
process_timeout_event() (or process_receive_event() ) and if it
encounters an error situation, will set an attempt to "try again
later" at time equal now + 10 seconds by setting
s->expire = now + 10;
This can happen at any time during the main event loop, which can end
up extending the user-specified timeout if "now + 10" is greater than
"start_time + user-specified-timeout".
I believe a patch like the following is needed to avoid this problem:
--- a/usr/kinit/ipconfig/main.c
+++ b/usr/kinit/ipconfig/main.c
@@ -437,6 +437,13 @@ static int loop(void)
if (timeout > s->expire - now.tv_sec)
timeout = s->expire - now.tv_sec;
+
+ /* Compensate for already-lost time */
+ gettimeofday(&now, NULL);
+ if (now.tv_sec + timeout > start + loop_timeout) {
+ timeout = loop_timeout - (now.tv_sec - start);
+ printf("Lowered timeout to match user request
= (%d s) \n", timeout);
+ }
}
I believe the current behaviour is buggy. This is confirmed when the
following line is executed:
if (loop_timeout >= 0 &&
now.tv_sec - start >= loop_timeout) {
printf("IP-Config: no response after %d "
"secs - giving up\n", loop_timeout);
rc = -1;
goto bail;
}
'loop_timeout' is the user-specified time-out. With a value of 2, in
case of error, this line prints:
IP-Config: no response after 2 secs - giving up
So it thinks that it waited 2 seconds - however, in reality it had
actually waited for 10 seconds.
The suggested code-change ensures that the timeout that is actually
used never exceeds the user-specified timeout.
[ Regression potential ]
This change ensures that user-specified timeouts are never exceeded, which is
a problem that appears to happen only in case of interface errors.
It may be that someone is relying on current behaviour where they receive
DHCP offers after their specified timeout (but within the 10-second error
timeout). However, 1) that is buggy behaviour and should be exposed. Such a
user would need to update their specified timeout to make it long enough to
receive the DHCP offer (setting the timeout to 10 would keep the existing
behaviour). 2) I think it is unlikely that such a scenario exists at all. The
10-second timeout problem happens when there are problems with the interface
that prevent it from even sending out the DHCP request. I think it is very
unlikely (or even, impossible) that DHCP offers would be received on a dead
interface.
Based on the above points, I consider the regression potential to be
very low for this change. I do not expect anyone who is currently
using ipconfig successfully to notice this change.
I believe the only difference introduced by this is the reduction of
delays caused by dead or problematic network interfaces. Those error
delays are shortened such that they never exceeed user-specified
timeouts.
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