Re: [Bug 1030] rte_malloc() and rte_free() get stuck when used with signal handler

["Mattias Rönnblom" <hofors@lysator.liu.se>]

On 2022-06-10 08:04, Sarosh Arif wrote:
> On Thu, Jun 9, 2022 at 8:26 PM Stephen Hemminger
> <stephen@networkplumber.org> wrote:
>>
>> On Thu, 09 Jun 2022 12:47:43 +0000
>> bugzilla@dpdk.org wrote:
>>
>>> https://bugs.dpdk.org/show_bug.cgi?id=1030
>>>
>>>              Bug ID: 1030
>>>             Summary: rte_malloc() and rte_free() get stuck when used with
>>>                      signal handler
>>>             Product: DPDK
>>>             Version: 22.03
>>>            Hardware: All
>>>                  OS: Linux
>>>              Status: UNCONFIRMED
>>>            Severity: normal
>>>            Priority: Normal
>>>           Component: core
>>>            Assignee: dev@dpdk.org
>>>            Reporter: sarosh.arif@emumba.com
>>>    Target Milestone: ---
>>>
>>> Created attachment 205
>>>    --> https://bugs.dpdk.org/attachment.cgi?id=205&action=edit
>>> calls rte_malloc and rte_free in the handler and main code
>>>
>>> I have a dpdk based application which uses rte_malloc() and rte_free()
>>> frequently in it's main code. The general method to close the application is
>>> though sending SIGINT. The application has a signal handler written for cleanup
>>> purposes before closing the application. The handler also uses rte_free() to
>>> release some of the memory during cleanup. The application gets stuck in a
>>> deadlock.
>>>
>>>
>>> Upon investigation I found out that both rte_free() and rte_malloc() use
>>> rte_spinlock_lock() function to place a lock on heap. While this lock is placed
>>> and the application receives SIGINT, it goes into the handler without releasing
>>> the lock. Since the handler itself calls rte_free() which tries to acquire the
>>> lock it gets stuck.
>>>
>>>
>>> I have attached a sample application to reproduce this problem.
>>>
>>>
>>> Steps to reproduce this problem:
>>>
>>> 1. compile the code provided in attachment with any version of dpdk
>>> 2. run the compiled binary
>>> 3. press ctrl+c till the prints stop
>>>
>>> Actual Results:
>>> The application gets stuck in either rte_free() or rte_malloc()
>>>
>>> Expected Results:
>>> Application should allocate and free the memory without getting stuck
>>>
>>
>> rte_malloc and rte_free are not async sigsafe()
>>
> Oh, I did not know that. This should be mentioned in the documentation.

Is there anything except <rte_atomic.h> that is/should be async-signal-safe?

>> but then again regular glibc is not either.
> Memory allocated with glibc malloc() is freed by itself upon closing
> the application. My application runs as a secondary process, and it
> needs to use rte_malloc() specifically because the memory should be
> shared between the two processes. If I don't free it upon closure it
> would just be leaked. Is there any other solution for it?

The standard solution is that the signal handler using some appropriate, 
async-signal-safe way talks to the main thread, which then goes on to 
cleanly terminate the application.

A write() to an fd, or an atomic store to a flag are two options.