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SubjectRe: [PATCH] proc/wchan: Use printk format instead of lookup_symbol_name()
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On 12/23/20 3:18 AM, Andrew Morton wrote:
> On Thu, 17 Dec 2020 17:54:13 +0100 Helge Deller <deller@gmx.de> wrote:
>
>> To resolve the symbol fuction name for wchan, use the printk format
>> specifier %ps instead of manually looking up the symbol function name
>> via lookup_symbol_name().
>>
>> Signed-off-by: Helge Deller <deller@gmx.de>
>>
>
> Please don't forget the "^---$" to separate the changelog from the
> diff.

Ok.

>
>> #include <linux/module.h>
>> @@ -386,19 +385,17 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
>> struct pid *pid, struct task_struct *task)
>> {
>> unsigned long wchan;
>> - char symname[KSYM_NAME_LEN];
>>
>> - if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
>> - goto print0;
>> + if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
>> + wchan = get_wchan(task);
>> + else
>> + wchan = 0;
>>
>> - wchan = get_wchan(task);
>> - if (wchan && !lookup_symbol_name(wchan, symname)) {
>> - seq_puts(m, symname);
>> - return 0;
>> - }
>> + if (wchan)
>> + seq_printf(m, "%ps", (void *) wchan);
>> + else
>> + seq_putc(m, '0');
>>
>> -print0:
>> - seq_putc(m, '0');
>> return 0;
>> }
>
> We can simplify this further?
>
> static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
> struct pid *pid, struct task_struct *task)
> {
> if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
> seq_printf(m, "%ps", (void *)get_wchan(task));
> else
> seq_putc(m, '0');
>
> return 0;
> }
>
>
> --- a/fs/proc/base.c~proc-wchan-use-printk-format-instead-of-lookup_symbol_name-fix
> +++ a/fs/proc/base.c
> @@ -384,15 +384,8 @@ static const struct file_operations proc
> static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
> struct pid *pid, struct task_struct *task)
> {
> - unsigned long wchan;
> -
> if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
> - wchan = get_wchan(task);
> - else
> - wchan = 0;
> -
> - if (wchan)
> - seq_printf(m, "%ps", (void *) wchan);
> + seq_printf(m, "%ps", (void *)get_wchan(task));
> else
> seq_putc(m, '0');

get_wchan() does return NULL sometimes, in which case with
your change now "0x0" instead of "0" gets printed.

If that's acceptable, then your patch is Ok.

Helge

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