Bug 60318 - ether_input() does things in wrong order in eCos
Summary: ether_input() does things in wrong order in eCos
Alias: None
Product: eCos
Classification: Retired
Component: TCPIP   
(Show other bugs)
Version: 1.5.2
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: eCos bugs internal list
QA Contact: eCos bugs internal list
Depends On:
TreeView+ depends on / blocked
Reported: 2002-02-25 15:16 UTC by Martin Buck
Modified: 2007-04-18 16:40 UTC (History)
0 users

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2003-06-20 16:13:49 UTC
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
Patch that fixes ether_input() bug (2.32 KB, patch)
2002-02-25 15:20 UTC, Martin Buck
no flags Details | Diff

Description Martin Buck 2002-02-25 15:16:29 UTC
From Bugzilla Helper:
User-Agent: Mozilla/4.76 [en] (WinNT; U)

Description of problem:
We implement a Ethernet-like network interface in our software. When we receive data on that interface, we call ether_input() to pass it to the IP stack just like in a 
standard BSD network driver. Depending on the priority of the thread that calls ether_input(), frames get stuck in ether_input() and are only passed on when the next 
frame arrives (which in turn gets stuck).
This is due to the fact that ether_input() first schedules processing of the frame by calling schednetisr(FOO) and then inserts it into the queue afterwards. This 
in OpenBSD since the kernel cannot be preempted, so processing starts after ether_input() inserted the frame into the queue and returned. It doesn't work in eCos 
since the call to schednetisr(FOO) might cause a context switch immediately before the frame is enqueued. The context switch only happens too early if you're 
ether_input() from a normal thread (as opposed to a DSR) and that thread's priority is lower that the network thread's priority. Unfortunately, both conditions are true 
for our software and are difficult to change.
The patch in the attachment fixes ether_input() so that it doesn't rely on being called from a DSR. It should not change ether_input()'s behaviour if it actually is called 
from a DSR.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
Difficult without a driver that doesn't use DSRs, but I hope my description and the patch are convincing enough :-)

Additional info:

Comment 1 Martin Buck 2002-02-25 15:20:08 UTC
Created attachment 46601 [details]
Patch that fixes ether_input() bug

Comment 2 Hugo Tyson 2002-02-28 14:21:22 UTC
I understand the problem, but since this only is a problem in somewhat
special circumstances, would it not be better simply to lock the scheduler
around the call to ether_input() in your application?  But that might spoil
latency for other operations...

Therefore I'll apply the patch you sent - thanks!

Comment 3 Martin Buck 2002-02-28 16:07:43 UTC
Right, ether_input() can potentially do a lot (especially when the Ethernet bridge is involved) and I wouldn't want to have the scheduler locked during 
the whole time.
Also, I spent quite some time to understand and find the problem. If somebody ever wants to implement another Ethernet-like driver running in a 
normal thread in the future (which might not be that uncommon in a RTOS), he shouldn't have to do the same again.

Comment 4 Alex Schuilenburg 2003-06-20 16:13:49 UTC
This bug has moved to http://bugs.ecos.sourceware.org/show_bug.cgi?id=60318

Note You need to log in before you can comment on or make changes to this bug.