Re: [PATCH] staging: ion: fix corruption of ion_import_dma_buf

[Laura Abbott <labbott@redhat.com>]

(adding Colin and John)

On 09/09/2015 12:41 AM, Shawn Lin wrote:
> we found this issue but still exit in lastest kernel. Simply
> keep ion_handle_create under mutex_lock to avoid this race.
>
> WARNING: CPU: 2 PID: 2648 at drivers/staging/android/ion/ion.c:512 ion_handle_add+0xb4/0xc0()
> ion_handle_add: buffer already found.
> Modules linked in: iwlmvm iwlwifi mac80211 cfg80211 compat
> CPU: 2 PID: 2648 Comm: TimedEventQueue Tainted: G        W    3.14.0 #7
>   00000000 00000000 9a3efd2c 80faf273 9a3efd6c 9a3efd5c 80935dc9 811d7fd3
>   9a3efd88 00000a58 812208a0 00000200 80e128d4 80e128d4 8d4ae00c a8cd8600
>   a8cd8094 9a3efd74 80935e0e 00000009 9a3efd6c 811d7fd3 9a3efd88 9a3efd9c
> Call Trace:
>    [<80faf273>] dump_stack+0x48/0x69
>    [<80935dc9>] warn_slowpath_common+0x79/0x90
>    [<80e128d4>] ? ion_handle_add+0xb4/0xc0
>    [<80e128d4>] ? ion_handle_add+0xb4/0xc0
>    [<80935e0e>] warn_slowpath_fmt+0x2e/0x30
>    [<80e128d4>] ion_handle_add+0xb4/0xc0
>    [<80e144cc>] ion_import_dma_buf+0x8c/0x110
>    [<80c517c4>] reg_init+0x364/0x7d0
>    [<80993363>] ? futex_wait+0x123/0x210
>    [<80992e0e>] ? get_futex_key+0x16e/0x1e0
>    [<8099308f>] ? futex_wake+0x5f/0x120
>    [<80c51e19>] vpu_service_ioctl+0x1e9/0x500
>    [<80994aec>] ? do_futex+0xec/0x8e0
>    [<80971080>] ? prepare_to_wait_event+0xc0/0xc0
>    [<80c51c30>] ? reg_init+0x7d0/0x7d0
>    [<80a22562>] do_vfs_ioctl+0x2d2/0x4c0
>    [<80b198ad>] ? inode_has_perm.isra.41+0x2d/0x40
>    [<80b199cf>] ? file_has_perm+0x7f/0x90
>    [<80b1a5f7>] ? selinux_file_ioctl+0x47/0xf0
>    [<80a227a8>] SyS_ioctl+0x58/0x80
>    [<80fb45e8>] syscall_call+0x7/0x7
>    [<80fb0000>] ? mmc_do_calc_max_discard+0xab/0xe4
>
> Fixes: 83271f626 ("ion: hold reference to handle...")
> Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
> ---
>
>   drivers/staging/android/ion/ion.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
> index eec878e..32e7b5c 100644
> --- a/drivers/staging/android/ion/ion.c
> +++ b/drivers/staging/android/ion/ion.c
> @@ -1179,13 +1179,13 @@ struct ion_handle *ion_import_dma_buf(struct ion_client *client, int fd)
>   		mutex_unlock(&client->lock);
>   		goto end;
>   	}
> -	mutex_unlock(&client->lock);
>
>   	handle = ion_handle_create(client, buffer);
> -	if (IS_ERR(handle))
> +	if (IS_ERR(handle)) {
> +		mutex_unlock(&client->lock);
>   		goto end;
> +	}
>
> -	mutex_lock(&client->lock);
>   	ret = ion_handle_add(client, handle);
>   	mutex_unlock(&client->lock);
>   	if (ret) {
>

So the patch looks correct but the locking change there seems like it was added
deliberately. Colin/John, do you remember why the locking for ion_import_dma_buf
changed? Was there a deadlock condition somewhere?

Thanks,
Laura