Discussion:
uclibc(1.0.12) mq_send return value and errno issue
Frank Liu
2016-11-18 03:43:45 UTC
Permalink
Hi All,

Kernel version : 4.4.19-linux4sam_5.4
uclibc version : 1.0.12
uclibc threading support : NPTL
Processor Arch: ARM

We create a NONBLOCKING message queue.

The expected behavior is when the message queue is full, calling mq_send would return -1 and set errno to EAGAIN(11). However we are seeing some inconsistent behaviors of mq_send.

When calling mq_send in a single threaded environment, the expected behavior is observed.

If the program starts a second thread, which is doing completely different task, calling mq_send when the queue is full would return -11 instead of -1. Also, the errno is set to an incorrect value. Values we have seen are 0, 2, which are completely different from the expected EAGAIN(11).

Frank
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Frank Liu
2016-11-18 06:45:53 UTC
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Please see the attached sample code.

If I turn READERS and WRITERS to 0, the test works fine.

Adding another thread in the process by setting a non-zero number to either READERS or WRITER, the test program crashes due to the assertion at line 99.

Regards

-----Original Message-----
From: Waldemar Brodkorb [mailto:***@uclibc-ng.org]
Sent: Friday, November 18, 2016 5:13 PM
To: Frank Liu
Cc: '***@uclibc.org'; ***@uclibc-ng.org; Dushara Jayasinghe (***@successful.com.au)
Subject: Re: uclibc(1.0.12) mq_send return value and errno issue

Hi,
Frank Liu wrote,
Post by Frank Liu
Hi All,
Kernel version : 4.4.19-linux4sam_5.4
uclibc version : 1.0.12
uclibc threading support : NPTL
Processor Arch: ARM
Better you switch to uClibc-ng mailinglist for this question.
Post by Frank Liu
We create a NONBLOCKING message queue.
The expected behavior is when the message queue is full, calling mq_send would return -1 and set errno to EAGAIN(11). However we are seeing some inconsistent behaviors of mq_send.
When calling mq_send in a single threaded environment, the expected behavior is observed.
If the program starts a second thread, which is doing completely different task, calling mq_send when the queue is full would return -11 instead of -1. Also, the errno is set to an incorrect value. Values we have seen are 0, 2, which are completely different from the expected EAGAIN(11).
Can you provide a simple test case to check the behaviour?

best regards
Waldemar
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Frank Liu
2016-11-25 03:52:28 UTC
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Hi Waldemar,

Thanks for the patchset. I can confirm it fixed my issue.

Regards
Frank

-----Original Message-----
From: Waldemar Brodkorb [mailto:***@uclibc-ng.org]
Sent: Thursday, November 24, 2016 2:27 PM
To: Frank Liu
Cc: Waldemar Brodkorb; '***@uclibc.org'; Dushara Jayasinghe (***@successful.com.au); ***@uclibc-ng.org
Subject: Re: uclibc(1.0.12) mq_send return value and errno issue

Hi Frank,
Frank Liu wrote,
Post by Frank Liu
Please see the attached sample code.
If I turn READERS and WRITERS to 0, the test works fine.
Adding another thread in the process by setting a non-zero number to either READERS or WRITER, the test program crashes due to the assertion at line 99.
I think I found the reason for the problem.

Try attached patch,

best regards
Waldemar
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