Re: [EDT][PATCH] kernel/exit.c : Fix missing read_unlock

Maninder Singh
2015-05-21T06:34:26Z

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EP-F6AA0618C49C4AEDA73BFF1B39950BAB
>> Hi,
>>
>> From: Maninder Singh <maninder1.s@samsung.com>
>>
>> Subject: [PATCH 1/1] kernel/exit.c : Fix missing task_unlock
>>
Subject: [PATCH 1/1] kernel/exit.c : Fix missing read_unlock

>> This patch adds missing read_unlock if do_wait_thread or ptrace_do_wait
>> returns non zero.

Reported By Prevent Under Missing unlock category(program hangs):-
missing_unlock: returning without unlocking tasklist_lock
>>
>> Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
>> Signed-off-by: Vaneet Narang <v.narang@samsung.com>
>> Reviewd-by: Akhilesh Kumar <akhilesh.k@samsung.com>
>> ---
>> kernel/exit.c | 8 ++++++--
>> 1 files changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/exit.c b/kernel/exit.c
>> index 22fcc05..31a061f 100644
>> --- a/kernel/exit.c
>> +++ b/kernel/exit.c
>> @@ -1486,12 +1486,16 @@ repeat:
>> tsk = current;
>> do {
>> retval = do_wait_thread(wo, tsk);
>> - if (retval)
>> + if (retval) {
>> + read_unlock(&tasklist_lock);
>> goto end;
>> + }
>>
>> retval = ptrace_do_wait(wo, tsk);
>> - if (retval)
>> + if (retval) {
>> + read_unlock(&tasklist_lock);
>> goto end;
>> + }
>>
>> if (wo->wo_flags & __WNOTHREAD)
>> break;
>
>That's surprising and the changelog is lacking.

>So the last time that code was touched upstream was 7 years ago:

> commit 64a16caf5e3417ee32f670debcb5857b02a9e08e
> Author: Oleg Nesterov <oleg@redhat.com>
> Date: Wed Jun 17 16:27:40 2009 -0700

> do_wait: simplify retval/tsk_result/notask_error mess

>please explain whether what you fix is:

> 1) an ancient bug that somehow nobody ever triggered (plus analysis
> of why it wasn't triggered)

> 2) a new bug introduced by commit XYZ (plus analysis)

> 3) something else

This issue is reported by Prevent Under category Missing Unlock, So we think it should be reported to maintainers.

>Thanks,
> Ingo

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