On 10/31/19 12:35 PM, John Garry wrote:
> On 16/10/2019 20:09, Jens Axboe wrote:
>> On 10/16/19 4:19 AM, John Garry wrote:
>>> With CONFIG_DEBUG_TEST_DRIVER_REMOVE set, we may find the following WARN:
>>>
>>> [ 23.452574] ------------[ cut here ]------------
>>> [ 23.457190] WARNING: CPU: 59 PID: 1 at drivers/ata/libata-core.c:6676 ata_host_detach+0x15c/0x168
>>> [ 23.466047] Modules linked in:
>>> [ 23.469092] CPU: 59 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc1-00010-g5b83fd27752b-dirty #296
>>> [ 23.477776] Hardware name: Huawei D06 /D06, BIOS Hisilicon D06 UEFI RC0 - V1.16.01 03/15/2019
>>> [ 23.486286] pstate: a0c00009 (NzCv daif +PAN +UAO)
>>> [ 23.491065] pc : ata_host_detach+0x15c/0x168
>>> [ 23.495322] lr : ata_host_detach+0x88/0x168
>>> [ 23.499491] sp : ffff800011cabb50
>>> [ 23.502792] x29: ffff800011cabb50 x28: 0000000000000007
>>> [ 23.508091] x27: ffff80001137f068 x26: ffff8000112c0c28
>>> [ 23.513390] x25: 0000000000003848 x24: ffff0023ea185300
>>> [ 23.518689] x23: 0000000000000001 x22: 00000000000014c0
>>> [ 23.523987] x21: 0000000000013740 x20: ffff0023bdc20000
>>> [ 23.529286] x19: 0000000000000000 x18: 0000000000000004
>>> [ 23.534584] x17: 0000000000000001 x16: 00000000000000f0
>>> [ 23.539883] x15: ffff0023eac13790 x14: ffff0023eb76c408
>>> [ 23.545181] x13: 0000000000000000 x12: ffff0023eac13790
>>> [ 23.550480] x11: ffff0023eb76c228 x10: 0000000000000000
>>> [ 23.555779] x9 : ffff0023eac13798 x8 : 0000000040000000
>>> [ 23.561077] x7 : 0000000000000002 x6 : 0000000000000001
>>> [ 23.566376] x5 : 0000000000000002 x4 : 0000000000000000
>>> [ 23.571674] x3 : ffff0023bf08a0bc x2 : 0000000000000000
>>> [ 23.576972] x1 : 3099674201f72700 x0 : 0000000000400284
>>> [ 23.582272] Call trace:
>>> [ 23.584706] ata_host_detach+0x15c/0x168
>>> [ 23.588616] ata_pci_remove_one+0x10/0x18
>>> [ 23.592615] ahci_remove_one+0x20/0x40
>>> [ 23.596356] pci_device_remove+0x3c/0xe0
>>> [ 23.600267] really_probe+0xdc/0x3e0
>>> [ 23.603830] driver_probe_device+0x58/0x100
>>> [ 23.608000] device_driver_attach+0x6c/0x90
>>> [ 23.612169] __driver_attach+0x84/0xc8
>>> [ 23.615908] bus_for_each_dev+0x74/0xc8
>>> [ 23.619730] driver_attach+0x20/0x28
>>> [ 23.623292] bus_add_driver+0x148/0x1f0
>>> [ 23.627115] driver_register+0x60/0x110
>>> [ 23.630938] __pci_register_driver+0x40/0x48
>>> [ 23.635199] ahci_pci_driver_init+0x20/0x28
>>> [ 23.639372] do_one_initcall+0x5c/0x1b0
>>> [ 23.643199] kernel_init_freeable+0x1a4/0x24c
>>> [ 23.647546] kernel_init+0x10/0x108
>>> [ 23.651023] ret_from_fork+0x10/0x18
>>> [ 23.654590] ---[ end trace 634a14b675b71c13 ]---
>>>
>>> With KASAN also enabled, we may also get many use-after-free reports.
>>>
>>> The issue is that when CONFIG_DEBUG_TEST_DRIVER_REMOVE is set, we may
>>> attempt to detach the ata_port before it has been probed.
>>>
>>> This is because the ata_ports are async probed, meaning that there is no
>>> guarantee that the ata_port has probed prior to detach. When the ata_port
>>> does probe in this scenario, we get all sorts of issues as the detach may
>>> have already happened.
>>>
>>> Fix by ensuring synchronisation with async_synchronize_full(). We could
>>> alternatively use the cookie returned from the ata_port probe
>>> async_schedule() call, but that means managing the cookie, so more
>>> complicated.
>>>
>>> Signed-off-by: John Garry <john.garry@xxxxxxxxxx>
>>> ---
>>> Note: This has only been boot tested and manual driver remove/add.
>>> My system has no disk attached to the ahci host.
>>>
>>> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
>>> index 28c492be0a57..74c9b3032d46 100644
>>> --- a/drivers/ata/libata-core.c
>>> +++ b/drivers/ata/libata-core.c
>>> @@ -6708,6 +6708,9 @@ void ata_host_detach(struct ata_host *host)
>>> {
>>> int i;
>>>
>>> + /* Ensure ata_port probe has completed */
>>> + async_synchronize_full();
>>> +
>>> for (i = 0; i < host->n_ports; i++)
>>> ata_port_detach(host->ports[i]);
>>>
>>>
>>
>> Nice debugging, and the fix looks appropriate to me. I don't think
>> there's any point in trying to individually synchronize cookies.
>> I'll let this simmer on the list for a day or two to let other folks
>> take a look at it, before queuing it up.
>>
>
> Hi Jens,
>
> FWIW, I did also now test this on qemu with an emulated disk and it was ok.
>
> Anyway, I don't mind if prefer to queue this early for 5.6 so it can sit
> on next for longer.
I've queued it up for 5.5, no point waiting one extra release :-)
--
Jens Axboe
