linux-kernel - Re: [PATCH] iscsi: Fix a sleep-in-atomic bug

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Date:   Fri, 02 Jun 2017 09:13:37 +0800
From:   Jia-Ju Bai <baijiaju1990@....com>
To:     "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
CC:     bart.vanassche@...disk.com, davem@...emloft.net, hare@...e.com,
        elfring@...rs.sourceforge.net, linux-scsi@...r.kernel.org,
        target-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iscsi: Fix a sleep-in-atomic bug

On 06/01/2017 02:21 PM, Nicholas A. Bellinger wrote:
> Hi Jia-Ju,
>
> On Wed, 2017-05-31 at 11:26 +0800, Jia-Ju Bai wrote:
>> The driver may sleep under a spin lock, and the function call path is:
>> iscsit_tpg_enable_portal_group (acquire the lock by spin_lock)
>>    iscsi_update_param_value
>>      kstrdup(GFP_KERNEL) -->  may sleep
>>
>> To fix it, the "GFP_KERNEL" is replaced with "GFP_ATOMIC".
>>
>> Signed-off-by: Jia-Ju Bai<baijiaju1990@....com>
>> ---
>>   drivers/target/iscsi/iscsi_target_parameters.c |    2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
> Btw, the use of tpg->tpg_state_lock in iscsit_tpg_enable_portal_group()
> while checking existing state and calling iscsi_update_param_value() is
> not necessary, since lio_target_tpg_enable_store() is already holding
> iscsit_get_tpg() ->  tpg->tpg_access_lock.
>
> How about the following instead to only take tpg->tpg_state_lock when
> updating tpg->tpg_state instead..?
>
> diff --git a/drivers/target/iscsi/iscsi_target_tpg.c b/drivers/target/iscsi/iscsi_target_tpg.c
> index 2e7e08d..abaabba 100644
> --- a/drivers/target/iscsi/iscsi_target_tpg.c
> +++ b/drivers/target/iscsi/iscsi_target_tpg.c
> @@ -311,11 +311,9 @@ int iscsit_tpg_enable_portal_group(struct iscsi_portal_group *tpg)
>          struct iscsi_tiqn *tiqn = tpg->tpg_tiqn;
>          int ret;
>
> -       spin_lock(&tpg->tpg_state_lock);
>          if (tpg->tpg_state == TPG_STATE_ACTIVE) {
>                  pr_err("iSCSI target portal group: %hu is already"
>                          " active, ignoring request.\n", tpg->tpgt);
> -               spin_unlock(&tpg->tpg_state_lock);
>                  return -EINVAL;
>          }
>          /*
> @@ -324,10 +322,8 @@ int iscsit_tpg_enable_portal_group(struct iscsi_portal_group *tpg)
>           * is enforced (as per default), and remove the NONE option.
>           */
>          param = iscsi_find_param_from_key(AUTHMETHOD, tpg->param_list);
> -       if (!param) {
> -               spin_unlock(&tpg->tpg_state_lock);
> +       if (!param)
>                  return -EINVAL;
> -       }
>
>          if (tpg->tpg_attrib.authentication) {
>                  if (!strcmp(param->value, NONE)) {
> @@ -341,6 +337,7 @@ int iscsit_tpg_enable_portal_group(struct iscsi_portal_group *tpg)
>                          goto err;
>          }
>
> +       spin_lock(&tpg->tpg_state_lock);
>          tpg->tpg_state = TPG_STATE_ACTIVE;
>          spin_unlock(&tpg->tpg_state_lock);
>
> @@ -353,7 +350,6 @@ int iscsit_tpg_enable_portal_group(struct iscsi_portal_group *tpg)
>          return 0;
>
>   err:
> -       spin_unlock(&tpg->tpg_state_lock);
>          return ret;
>   }
>
I think it is fine to me.

Thanks,
Jia-Ju Bai