Re: [PATCH v16 01/14] power: reset: reboot-mode: Synchronize list traversal

[Shivendra Pratap <shivendra.pratap@oss.qualcomm.com>]

On 10/15/2025 8:02 PM, Bartosz Golaszewski wrote:
> On Wed, 15 Oct 2025 at 06:38, Shivendra Pratap
> <shivendra.pratap@oss.qualcomm.com> wrote:
>>
>> List traversals must be synchronized to prevent race conditions
>> and data corruption. The reboot-mode list is not protected by a
>> lock currently, which can lead to concurrent access and race.
>>
>> Introduce a mutex lock to guard all operations on the reboot-mode
>> list and ensure thread-safe access. The change prevents unsafe
>> concurrent access on reboot-mode list.
>>
>> Fixes: 4fcd504edbf7 ("power: reset: add reboot mode driver")
>> Fixes: ca3d2ea52314 ("power: reset: reboot-mode: better compatibility with DT (replace ' ,/')")
>>
>> Signed-off-by: Shivendra Pratap <shivendra.pratap@oss.qualcomm.com>
>> ---
>>  drivers/power/reset/reboot-mode.c | 96 +++++++++++++++++++++------------------
>>  include/linux/reboot-mode.h       |  4 ++
>>  2 files changed, 57 insertions(+), 43 deletions(-)
>>
>> diff --git a/drivers/power/reset/reboot-mode.c b/drivers/power/reset/reboot-mode.c
>> index fba53f638da04655e756b5f8b7d2d666d1379535..8fc3e14638ea757c8dc3808c240ff569cbd74786 100644
>> --- a/drivers/power/reset/reboot-mode.c
>> +++ b/drivers/power/reset/reboot-mode.c
>> @@ -29,9 +29,11 @@ static unsigned int get_reboot_mode_magic(struct reboot_mode_driver *reboot,
>>         if (!cmd)
>>                 cmd = normal;
>>
>> -       list_for_each_entry(info, &reboot->head, list)
>> -               if (!strcmp(info->mode, cmd))
>> -                       return info->magic;
>> +       scoped_guard(mutex, &reboot->rb_lock) {
>> +               list_for_each_entry(info, &reboot->head, list)
>> +                       if (!strcmp(info->mode, cmd))
>> +                               return info->magic;
>> +       }
>>
>>         /* try to match again, replacing characters impossible in DT */
>>         if (strscpy(cmd_, cmd, sizeof(cmd_)) == -E2BIG)
>> @@ -41,9 +43,11 @@ static unsigned int get_reboot_mode_magic(struct reboot_mode_driver *reboot,
>>         strreplace(cmd_, ',', '-');
>>         strreplace(cmd_, '/', '-');
>>
>> -       list_for_each_entry(info, &reboot->head, list)
>> -               if (!strcmp(info->mode, cmd_))
>> -                       return info->magic;
>> +       scoped_guard(mutex, &reboot->rb_lock) {
>> +               list_for_each_entry(info, &reboot->head, list)
>> +                       if (!strcmp(info->mode, cmd_))
>> +                               return info->magic;
>> +       }
>>
>>         return 0;
>>  }
>> @@ -78,46 +82,50 @@ int reboot_mode_register(struct reboot_mode_driver *reboot)
>>
>>         INIT_LIST_HEAD(&reboot->head);
>>
>> -       for_each_property_of_node(np, prop) {
>> -               if (strncmp(prop->name, PREFIX, len))
>> -                       continue;
>> -
>> -               info = devm_kzalloc(reboot->dev, sizeof(*info), GFP_KERNEL);
>> -               if (!info) {
>> -                       ret = -ENOMEM;
>> -                       goto error;
>> -               }
>> -
>> -               if (of_property_read_u32(np, prop->name, &info->magic)) {
>> -                       dev_err(reboot->dev, "reboot mode %s without magic number\n",
>> -                               info->mode);
>> -                       devm_kfree(reboot->dev, info);
>> -                       continue;
>> -               }
>> -
>> -               info->mode = kstrdup_const(prop->name + len, GFP_KERNEL);
>> -               if (!info->mode) {
>> -                       ret =  -ENOMEM;
>> -                       goto error;
>> -               } else if (info->mode[0] == '\0') {
>> -                       kfree_const(info->mode);
>> -                       ret = -EINVAL;
>> -                       dev_err(reboot->dev, "invalid mode name(%s): too short!\n",
>> -                               prop->name);
>> -                       goto error;
>> +       mutex_init(&reboot->rb_lock);
>> +
>> +       scoped_guard(mutex, &reboot->rb_lock) {
>> +               for_each_property_of_node(np, prop) {
>> +                       if (strncmp(prop->name, PREFIX, len))
>> +                               continue;
>> +
>> +                       info = devm_kzalloc(reboot->dev, sizeof(*info), GFP_KERNEL);
>> +                       if (!info) {
>> +                               ret = -ENOMEM;
>> +                               goto error;
>> +                       }
>> +
>> +                       if (of_property_read_u32(np, prop->name, &info->magic)) {
>> +                               dev_err(reboot->dev, "reboot mode %s without magic number\n",
>> +                                       info->mode);
>> +                               devm_kfree(reboot->dev, info);
>> +                               continue;
>> +                       }
>> +
>> +                       info->mode = kstrdup_const(prop->name + len, GFP_KERNEL);
>> +                       if (!info->mode) {
>> +                               ret =  -ENOMEM;
>> +                               goto error;
>> +                       } else if (info->mode[0] == '\0') {
>> +                               kfree_const(info->mode);
>> +                               ret = -EINVAL;
>> +                               dev_err(reboot->dev, "invalid mode name(%s): too short!\n",
>> +                                       prop->name);
>> +                               goto error;
>> +                       }
>> +
>> +                       list_add_tail(&info->list, &reboot->head);
> 
> This seems to be the only call that actually needs synchronization.
> All of the above can be run outside the critical section.

sure. will add it only around the required lines.

> 
>>                 }
>>
>> -               list_add_tail(&info->list, &reboot->head);
>> -       }
>> -
>> -       reboot->reboot_notifier.notifier_call = reboot_mode_notify;
>> -       register_reboot_notifier(&reboot->reboot_notifier);
>> +               reboot->reboot_notifier.notifier_call = reboot_mode_notify;
>> +               register_reboot_notifier(&reboot->reboot_notifier);
>>
>> -       return 0;
>> +               return 0;
>>
>>  error:
>> -       list_for_each_entry(info, &reboot->head, list)
>> -               kfree_const(info->mode);
>> +               list_for_each_entry(info, &reboot->head, list)
>> +                       kfree_const(info->mode);
>> +       }
>>
>>         return ret;
>>  }
>> @@ -133,8 +141,10 @@ int reboot_mode_unregister(struct reboot_mode_driver *reboot)
>>
>>         unregister_reboot_notifier(&reboot->reboot_notifier);
>>
>> -       list_for_each_entry(info, &reboot->head, list)
>> -               kfree_const(info->mode);
>> +       scoped_guard(mutex, &reboot->rb_lock) {
>> +               list_for_each_entry(info, &reboot->head, list)
>> +                       kfree_const(info->mode);
>> +       }
> 
> Please destroy the mutex here.

sure thanks. will add destroy here.

thanks,
Shivendra