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SubjectRe: [PATCH] do_fork(): Rename 'stack_size' argument to reflect actual use

On 05/03/15 01:07, David Rientjes wrote:
> On Wed, 4 Mar 2015, Alex Dowad wrote:
>
>> The 'stack_size' argument is never used to pass a stack size. It's only used when
>> forking a kernel thread, in which case it is an argument which should be passed
>> to the 'main' function which the kernel thread executes. Hence, rename it to
>> 'kthread_arg'.
>>
>> Signed-off-by: Alex Dowad <alexinbeijing@gmail.com>
>> ---
>>
>> Hi,
>>
>> Please have a look at this patch. If this is accepted, I have a series of patches
>> ready for a similar cleanup to all the arch-specific implementations of copy_thread()
>> (as suggested by Andrew Morton in a private e-mail).
>>
>> Thank you,
>> Alex Dowad
>>
>> kernel/fork.c | 14 ++++++++------
>> 1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/kernel/fork.c b/kernel/fork.c
>> index cf65139..b38a2ae 100644
>> --- a/kernel/fork.c
>> +++ b/kernel/fork.c
>> @@ -1186,10 +1186,12 @@ init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
>> * It copies the registers, and all the appropriate
>> * parts of the process environment (as per the clone
>> * flags). The actual kick-off is left to the caller.
>> + *
>> + * When copying a kernel thread, 'stack_start' is the function to run.
>> */
>> static struct task_struct *copy_process(unsigned long clone_flags,
>> unsigned long stack_start,
>> - unsigned long stack_size,
>> + unsigned long kthread_arg,
>> int __user *child_tidptr,
>> struct pid *pid,
>> int trace)
>> @@ -1401,7 +1403,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>> retval = copy_io(clone_flags, p);
>> if (retval)
>> goto bad_fork_cleanup_namespaces;
>> - retval = copy_thread(clone_flags, stack_start, stack_size, p);
>> + retval = copy_thread(clone_flags, stack_start, kthread_arg, p);
>> if (retval)
>> goto bad_fork_cleanup_io;
>>
>> @@ -1629,8 +1631,8 @@ struct task_struct *fork_idle(int cpu)
>> * it and waits for it to finish using the VM if required.
>> */
>> long do_fork(unsigned long clone_flags,
>> - unsigned long stack_start,
>> - unsigned long stack_size,
>> + unsigned long stack_start, /* or function for kthread to run */
>> + unsigned long kthread_arg,
>> int __user *parent_tidptr,
>> int __user *child_tidptr)
>> {
> Looks fine, but I'm not sure about commenting functional formals. Since
> copy_process() and do_fork() can have formals with different meanings,
> then why not just rename them "arg1" and "arg2" respectively and then
> define in the comment above the function what the possible combinations
> are?

The second argument is *only* ever used for one thing: an argument
passed to a kernel thread. That's why I would like to rename it to
"kthread_arg". The previous argument (currently named "stack_start") is
indeed used for 2 different things: a new stack pointer for a user
thread, or a function to be executed by a kernel thread. Rather than
"arg1", what would you think of something like "sp_or_fn", or "usp_or_fn"?

Thanks for your feedback!

>
>> @@ -1656,7 +1658,7 @@ long do_fork(unsigned long clone_flags,
>> trace = 0;
>> }
>>
>> - p = copy_process(clone_flags, stack_start, stack_size,
>> + p = copy_process(clone_flags, stack_start, kthread_arg,
>> child_tidptr, NULL, trace);
>> /*
>> * Do this prior waking up the new thread - the thread pointer
>> @@ -1740,7 +1742,7 @@ SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
>> int, tls_val)
>> #elif defined(CONFIG_CLONE_BACKWARDS3)
>> SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
>> - int, stack_size,
>> + int, ignored,
>> int __user *, parent_tidptr,
>> int __user *, child_tidptr,
>> int, tls_val)



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