crypto: pcrypt - Fix hungtask for PADATA_RESET

In the Linux kernel, the following vulnerability has been resolved:

crypto: pcrypt - Fix hungtask for PADATA_RESET

We found a hungtask bug in test_aead_vec_cfg as follows:

INFO: task cryptomgr_test:391009 blocked for more than 120 seconds.

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

Call trace:

__switch_to+0x98/0xe0

__schedule+0x6c4/0xf40

schedule+0xd8/0x1b4

schedule_timeout+0x474/0x560

wait_for_common+0x368/0x4e0

wait_for_completion+0x20/0x30

wait_for_completion+0x20/0x30

test_aead_vec_cfg+0xab4/0xd50

test_aead+0x144/0x1f0

alg_test_aead+0xd8/0x1e0

alg_test+0x634/0x890

cryptomgr_test+0x40/0x70

kthread+0x1e0/0x220

ret_from_fork+0x10/0x18

Kernel panic - not syncing: hung_task: blocked tasks

For padata_do_parallel, when the return err is 0 or -EBUSY, it will call

wait_for_completion(&wait->completion) in test_aead_vec_cfg. In normal

case, aead_request_complete() will be called in pcrypt_aead_serial and the

return err is 0 for padata_do_parallel. But, when pinst->flags is

PADATA_RESET, the return err is -EBUSY for padata_do_parallel, and it

won't call aead_request_complete(). Therefore, test_aead_vec_cfg will

hung at wait_for_completion(&wait->completion), which will cause

hungtask.

The problem comes as following:

(padata_do_parallel) |

rcu_read_lock_bh(); |

err = -EINVAL; | (padata_replace)

| pinst->flags |= PADATA_RESET;

err = -EBUSY |

if (pinst->flags & PADATA_RESET) |

rcu_read_unlock_bh() |

return err

In order to resolve the problem, we replace the return err -EBUSY with

-EAGAIN, which means parallel_data is changing, and the caller should call

it again.

v3:

remove retry and just change the return err.

v2:

introduce padata_try_do_parallel() in pcrypt_aead_encrypt and

pcrypt_aead_decrypt to solve the hungtask.