Bug 78968 - FreeBSD freezes on mbufs exhaustion (network interface independent)
Summary: FreeBSD freezes on mbufs exhaustion (network interface independent)
Status: Open
Alias: None
Product: Base System
Classification: Unclassified
Component: kern (show other bugs)
Version: Unspecified
Hardware: Any Any
: Normal Affects Only Me
Assignee: freebsd-bugs (Nobody)
Depends on:
Reported: 2005-03-17 22:40 UTC by Jakub Kruszona-Zawadzki
Modified: 2019-06-13 01:51 UTC (History)
1 user (show)

See Also:


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Description Jakub Kruszona-Zawadzki 2005-03-17 22:40:02 UTC
We are using all of our output bandwidth. Tcp stack allocates mbufs for output queues. When mbufs space is exhausted system freezes. Even 'numlock' on keyboard don't work. It looks like kernel is going into an infinite loop or something - system is dead and the only thing you can do is reboot.


This problem doesn't exist in FreeBSD 4.x
How-To-Repeat: Set max mbufs to a small number (only for testing).
Generate a file about 300kB (i.e. dd if=/dev/urandom of=/tmp/file bs=1024 count=300).
Add to inetd.conf line like this:
telnet  stream  tcp     nowait  root    /bin/cat        cat     /tmp/file
Restart inetd with these options (maybe not all are necessary):
inetd -c 0 -C 0 -R 0 -s 0

On remote machine run many processes that will open many connections to your serwer on telent port, but WILL NOT download the file. You can use these programs:
In python:
#!/usr/bin/env python
from socket import socket
from time import sleep

socks = []
for i in xrange(240):
        s = socket()
    except Exception:

print "opened"

for i in socks:

In php:
 for ($i=0;$i<1000;$i++) {

FreeBSD 5.3 with default number of mbufs (about 17000) freezes after a few minutes, when both these programs work in several (6 pythons an 15 phps) copies.
While these programs are active, "netstat -n" should be showing many "ESTABLISHED" connections with full output queue. In "netstat -m" output number of "mbufs in use" and "mbuf clusters in use" should increase. When current number of "mbuf clusters in use" reaches max value, system freezes in a few seconds.

During normal work "netstat -m" looks like this:
334 mbufs in use
198/17088 mbuf clusters in use (current/max)
0/3/4528 sfbufs in use (current/peak/max)
479 KBytes allocated to network
0 requests for sfbufs denied
0 requests for sfbufs delayed
0 requests for I/O initiated by sendfile
104 calls to protocol drain routines
Comment 1 Ernie Smallis 2005-05-17 19:41:47 UTC
I am seeing this too:

The fxp driver is receiving a return of ENOBUFS from m_getcl() (no surprise 
there).  However, since there are no clusters available and the fxp driver 
has frames to DMA from its FIFO; it keeps calling for clusters which never 
happens successfully.  It appears the system is hung but; in fact, it is in a 
tight loop.

I believe BSD 4.x had a patch that fixed a panic for the exhaustion situation 
since the code would be de-referencing a NULL pointer.  So, now we have a 
test for NULL and the return of ENOBUFS.  That's one way of not seeing the 
current problem ;-)

Another way is to fix this.  The test for NULL is certainly appropriate 
however, what happens next isn't.   I am looking to contact the relevant  
committer(s) for a discussion as to how to resolve this problem.


Ernie ;-)
Comment 2 George V. Neville-Neil freebsd_committer 2006-11-12 09:52:00 UTC
Responsible Changed
From-To: freebsd-bugs->gnn

This shoiuld be verified or closed.
Comment 3 George V. Neville-Neil freebsd_committer 2010-06-15 18:35:12 UTC
Responsible Changed
From-To: gnn->freebsd-net

5.3 bug, probably no longer relevant.
Comment 4 Eitan Adler freebsd_committer freebsd_triage 2017-12-31 07:59:45 UTC
For bugs matching the following criteria:

Status: In Progress Changed: (is less than) 2014-06-01

Reset to default assignee and clear in-progress tags.

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