linux-kernel - Re: [PATCH timers/core] posix-cpu-timers: Put the task_struct in posix_cpu_timers

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Date:   Wed, 04 Mar 2020 09:56:37 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>, Qian Cai <cai@....pw>
Cc:     oleg@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH timers/core] posix-cpu-timers: Put the task_struct in posix_cpu_timers_create

ebiederm@...ssion.com (Eric W. Biederman) writes:

> Qian Cai <cai@....pw> writes:
>> The recent commit removed put_task_struct() in posix_cpu_timer_del()
>> results in many memory leaks like this,
>>
>> unreferenced object 0xc0000016d9b44480 (size 8192):
>>   comm "timer_create01", pid 57749, jiffies 4295163733 (age 6159.670s)
>>   hex dump (first 32 bytes):
>>     02 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00  ................
>>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>   backtrace:
>>     [<0000000056aca129>] copy_process+0x26c/0x18e0
>>     alloc_task_struct_node at kernel/fork.c:169
>>     (inlined by) dup_task_struct at kernel/fork.c:877
>>     (inlined by) copy_process at kernel/fork.c:1929
>>     [<00000000bdbbf9f8>] _do_fork+0xac/0xb20
>>     [<00000000dcb1c445>] __do_sys_clone+0x98/0xe0
>>     __do_sys_clone at kernel/fork.c:2591
>>     [<000000006c059205>] ppc_clone+0x8/0xc
>>     ppc_clone at arch/powerpc/kernel/entry_64.S:479
>>
>
> I forgot that get_task_for_clock called by posix_cpu_timer_create
> returns a reference to a task_struct.  Put that reference
> to avoid the leak.

I took the liberty to fold this back into the affected commit and add a
comment why this put_task_struct() is actually required.

Thanks,

        tglx