Deadlock in v2.6.2

[Barry-Xu-2018]

Is there an already existing issue for this?

• I have searched the existing issues

Expected behavior

No deadlock occurs at startup

Current behavior

A high deadlock rate occurs at startup.

Steps to reproduce

The scenario while deadlock occurs.

##1 Get a lock on mp_mutex in Thread3
##2 Get shared lock of endpoints_list_mutex in Thread2
##3 Trying to get mp_mutex in Thread2, but it is blocked because it is already locked in Thread3
##4 Trying to get write lock of endpoints_list_mutex in Thread1, but it is blocked because there is a reader in ##2.

Fast-DDS/include/fastrtps/utils/shared_mutex.hpp

Lines 69 to 72 in 5076ebc

	while (state_ & n_readers_)
	{
	gate2_.wait(lk);
	}

write_entered flag is set, and following endpoints_list_mutex reads are blocked.

Fast-DDS/include/fastrtps/utils/shared_mutex.hpp

Lines 98 to 101 in 5076ebc

	while ((state_ & write_entered_) || (state_ & n_readers_) == n_readers_)
	{
	gate1_.wait(lk);
	}

##5 Trying to get shared lock of endpoints_list_mutex in Thread3, but it is blocked because of the write_entered flag

Fast DDS version/commit

v2.6.2

Platform/Architecture

Ubuntu Focal 20.04 amd64

Transport layer

Default configuration, UDPv4 & SHM

Additional context

For same codes, there is no deadlock with v2.6.0

XML configuration file

No response

Relevant log output

No response

Network traffic capture

No response

[fujitatomoya]

@MiguelCompany @eProsima/team this is deadlock issue, just friendly ping.

[MiguelCompany]

@Barry-Xu-2018 @fujitatomoya There's a proposed fix in #2976, could you check with it?

[fujitatomoya]

@MiguelCompany thanks! we will try that out and get back to you.

[MiguelCompany]

@Barry-Xu-2018 @fujitatomoya Did you have time to check whether #2976 fixes this?

[fujitatomoya]

@MiguelCompany i will check the evaluation status, will get back to you soon.

[Barry-Xu-2018]

@MiguelCompany According to changed code, I think it can fix this problem. Fujita-san will provide final evaluation result in the real environment.

[fujitatomoya]

Fujita-san

that is me 😄 family name!

[wade30822]

@fujitatomoya hello，how is the final evaluation about #2976 going？

[fujitatomoya]

sorry we confirmed that no deadlock observed after this PR.

[wade30822]

@fujitatomoya thx～

[MiguelCompany]

Closing based on #2961 (comment)