Re: [PATCH] s390: correct misuses of module_put in appldata_generic_handler.

Zhouyi Zhou
2014-03-19T00:59:42Z

Delicate design! thanks for replying, sorry for the trouble

On Tue, Mar 18, 2014 at 9:34 PM, Gerald Schaefer
<gerald.schaefer@de.ibm.com> wrote:
> On Tue, 18 Mar 2014 09:24:55 +0800
> Zhouyi Zhou <zhouzhouyi@gmail.com> wrote:
>
>> Thanks Gerald for reviewing and sorry for not elaborated it in the e-mail.
>>
>> Firstly, I think you can't call module_put after fail try_module_get
>
> There is another try_module_get() in this function before that, so I need
> to call module_put() once if the second try_module_get() fails.
>
> The first try_module_get() is only needed within the function, while the
> second one is needed to prevent a module from being unloaded while its
> callback is registered, so that reference is kept as long as the module
> is active.
>
>>
>> Secondly, there exists duplicate module_put on the program path (the last
>> one is before return 0)
>
> There is one module_put() for every try_module_get(). If "1" is written
> to the sysctl, the function exits with one "missing" module_put(), which
> is held to protect the callback. When "0" is written, this reference
> is returned again with an "extra" module_put().
>
>>
>> On Mon, Mar 17, 2014 at 9:28 PM, Gerald Schaefer
>> <gerald.schaefer@de.ibm.com> wrote:
>> > On Sat, 15 Mar 2014 21:35:40 +0800
>> > Zhouyi Zhou <zhouzhouyi@gmail.com> wrote:
>> >
>> >> correct misuses of module_put in appldata_generic_handler
>> >
>> > Sorry, I don't see any misuse, could you elaborate?
>> >
>> >>
>> >> Signed-off-by: Zhouyi Zhou <yizhouzhou@ict.ac.cn>
>> >> ---
>> >> arch/s390/appldata/appldata_base.c | 3 ---
>> >> 1 file changed, 3 deletions(-)
>> >>
>> >> diff --git a/arch/s390/appldata/appldata_base.c b/arch/s390/appldata/appldata_base.c
>> >> index 47c8630..683e0282 100644
>> >> --- a/arch/s390/appldata/appldata_base.c
>> >> +++ b/arch/s390/appldata/appldata_base.c
>> >> @@ -343,7 +343,6 @@ appldata_generic_handler(struct ctl_table *ctl, int write,
>> >> // protect work queue callback
>> >> if (!try_module_get(ops->owner)) {
>> >> mutex_unlock(&appldata_ops_mutex);
>> >> - module_put(ops->owner);
>> >> return -ENODEV;
>> >> }
>> >> ops->callback(ops->data); // init record
>> >> @@ -354,7 +353,6 @@ appldata_generic_handler(struct ctl_table *ctl, int write,
>> >> if (rc != 0) {
>> >> pr_err("Starting the data collection for %s "
>> >> "failed with rc=%d\n", ops->name, rc);
>> >> - module_put(ops->owner);
>> >> } else
>> >> ops->active = 1;
>> >> } else if ((buf[0] == '0') && (ops->active == 1)) {
>> >> @@ -365,7 +363,6 @@ appldata_generic_handler(struct ctl_table *ctl, int write,
>> >> if (rc != 0)
>> >> pr_err("Stopping the data collection for %s "
>> >> "failed with rc=%d\n", ops->name, rc);
>> >> - module_put(ops->owner);
>> >> }
>> >> mutex_unlock(&appldata_ops_mutex);
>> >> out:
>> >
>> --
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>