Re: [PATCH] libata: Ensure ata_port probe has completed before detach

From: Jens Axboe
Date: Wed Oct 16 2019 - 15:10:02 EST

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.

--
Jens Axboe