2009-03-11 07:59:16     Problem with Shared Memory IPC

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2009-03-11 07:59:16     Problem with Shared Memory IPC

der knut (GERMANY)

Message: 70770   

 

Hello,

 

as described at

 

https://blackfin.uclinux.org/gf/project/uclinux-dist/forum/?action=ForumBrowse&forum_id=39&_forum_action=ForumMessageBrowse&thread_id=32758

 

and tracker item #4948 I am looking for a problem with shared memory.

 

It seem that the shared memory was reused by kernel or something else.

 

1) Latest Kernel SVN revision 6167; MPU disabled

 

2) Toolchain SVN snapshot Feb. 2009

 

3) Start linux on BF526 Rev 0.0 custom board with root mounted with nfs (every fs action == ethernet action)

 

4) Test app. from bug tracker item #4948 (shmtest.c)

 

5) Start "shmtest r" at console

 

6) Start "shmtest w" at first telnet session and type "testtesttest"

 

7) On console / "shmtest r" outout is

 

testtestte

testtestte

testtestte

testtestte

 

.......

 

as expected.

 

8) I do some memory operations, like

 

echo 3 > /proc/sys/vm/drop_caches

 

copy some files

 

echo 3 > /proc/sys/vm/drop_caches

 

for several times on a second telnet session.

 

9) Output of "shmtest r" change

 

.....

testtestte

testtestte

testtestte

testtestte

testtestte

testtestte

testtestte

testtestte

H�

H�

H�

H�

H�

H�

H�

H�

........

 

 

 

It look like something wrote on shared memory while "shmtest" own this memory.

 

If I type something else to "shmtest w" everything is looking fine again as long as I use some cache and free it like described above. After a while running the system the error disappear, it seems that shared memory is in stable use by something other and not any longer used by cache (?).

 

This also happend if we start our applications, I reduce the problem like described above to exclude our code.

 

What I am doing wrong?

 

Thanks a lot

 

Knut

 

 

 

 

 

 

 

 

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2009-03-11 22:31:34     Re: Problem with Shared Memory IPC

Mike Frysinger (UNITED STATES)

Message: 70805   

 

can you try this patch and see if it fixes things ?

 

thread.gmane.org/gmane.linux.hardware.blackfin.kernel.devel/1275

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2009-03-12 15:44:00     Re: Problem with Shared Memory IPC

der knut (GERMANY)

Message: 70884   

 

Hello,

 

thanks a lot for fast and excellent help.

 

Now it works.

 

Thanks

 

Knut

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