linux-kernel - Re: [PATCH] staging: ion: fix corruption of ion_import_dma

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Message-ID: <55F1B36C.1050605@redhat.com>
Date:	Thu, 10 Sep 2015 09:44:28 -0700
From:	Laura Abbott <labbott@...hat.com>
To:	Colin Cross <ccross@...roid.com>
Cc:	Shawn Lin <shawn.lin@...k-chips.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>
Subject: Re: [PATCH] staging: ion: fix corruption of ion_import_dma_buf

On 09/09/2015 10:41 PM, Colin Cross wrote:
> On Wed, Sep 9, 2015 at 10:19 AM, Laura Abbott <labbott@...hat.com> wrote:
>> (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@...k-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
>
> I can't see any reason to not hold the mutex across ion_handle_create.
> The patch that introduced the bug
> (83271f6262c91a49df325c52bec8f00f4de294ca, ion: hold reference to
> handle after ion_uhandle_get) required that the mutex not be held
> around the call to ion_handle_put, but didn't affect
> ion_handle_create.

Thanks for confirming. With that,

Reviewed-by: Laura Abbott <labbott@...hat.com>

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