Re: [Bugme-new] [Bug 10737] New: pktgen procfs problem

Eric W. Biederman wrote:

Patrick McHardy [off-list ref] writes:

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Patrick McHardy wrote:

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I've been looking into the same problem, without much success so
far. The problem appears to affect any /proc/net file, but not
files outside of /proc/net, so I'm guessing its net-ns related.
A testcase found by Ben Greear is opening the file multiple times:

# /tmp/open /proc/net/kpktgen_0

=> refcnt goes to 1

^C

=> refcnt goes to 0

Without ^C and opening the file a second time:

# /tmp/open /proc/net/kpktgen_0

=> refcnt goes to 2 (sometimes also 11)

^C

=> refcnt stays at previous value.

The refcnt even leaks if the file can't be successfully opened,
for example because of lacking permissions.

How are you reading the refcount on kpktgen_0? Just a printk in the
kernel code?

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Some more information: the problem seems to occur only if
the file is opened by two different processes.

I'm starting a bisection now.

git-bisect identified e9720acd ([NET]: Make /proc/net a symlink
on /proc/self/net (v3)) as the guilty commit. I couldn't find
the problem in that commit, so someone with a better understanding
of how this is supposed to work should look into it.

To recap:
- The problem is that we get complaints from remove_proc_entry
  on unload of the pktgen module.

- The problem appears to only happen when multiple processes open the file.

- The problem only appears after we moved /proc/net into /proc/<pid>/net

Just to be clear, the problem I saw with too many refs would not even let
me remove a module.  They may be the same root problem, but not necessarily.

I also saw the problem on multiple modules with proc/net/ file systems,
not just pktgen.

The part about multiple processes opening the file is definitely true
with my bug report, but based on email I saw, I'm not sure it is true for
the remove_proc_entry problem reported by someone else.

Thanks,
Ben


-- 
Ben Greear [off-list ref]
Candela Technologies Inc  http://www.candelatech.com