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SubjectRe: [PATCH] firmware: coreboot: Register bus in module init
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On 10/19/22 18:10, Brian Norris wrote:
> The coreboot_table driver registers a coreboot bus while probing a
> "coreboot_table" device representing the coreboot table memory region.
> Probing this device (i.e., registering the bus) is a dependency for the
> module_init() functions of any driver for this bus (e.g.,
> memconsole-coreboot.c / memconsole_driver_init()).
>
> With synchronous probe, this dependency works OK, as the link order in
> the Makefile ensures coreboot_table_driver_init() (and thus,
> coreboot_table_probe()) completes before a coreboot device driver tries
> to add itself to the bus.
>
> With asynchronous probe, however, coreboot_table_probe() may race with
> memconsole_driver_init(), and so we're liable to hit one of these two:
>
> 1. coreboot_driver_register() eventually hits "[...] the bus was not
> initialized.", and the memconsole driver fails to register; or
> 2. coreboot_driver_register() gets past #1, but still races with
> bus_register() and hits some other undefined/crashing behavior (e.g.,
> in driver_find() [1])
>
> We can resolve this by registering the bus in our initcall, and only
> deferring "device" work (scanning the coreboot memory region and
> creating sub-devices) to probe().
>
> [1] Example failure, using 'driver_async_probe=*' kernel command line:
>
> [ 0.114217] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
> ...
> [ 0.114307] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 6.1.0-rc1 #63
> [ 0.114316] Hardware name: Google Scarlet (DT)
> ...
> [ 0.114488] Call trace:
> [ 0.114494] _raw_spin_lock+0x34/0x60
> [ 0.114502] kset_find_obj+0x28/0x84
> [ 0.114511] driver_find+0x30/0x50
> [ 0.114520] driver_register+0x64/0x10c
> [ 0.114528] coreboot_driver_register+0x30/0x3c
> [ 0.114540] memconsole_driver_init+0x24/0x30
> [ 0.114550] do_one_initcall+0x154/0x2e0
> [ 0.114560] do_initcall_level+0x134/0x160
> [ 0.114571] do_initcalls+0x60/0xa0
> [ 0.114579] do_basic_setup+0x28/0x34
> [ 0.114588] kernel_init_freeable+0xf8/0x150
> [ 0.114596] kernel_init+0x2c/0x12c
> [ 0.114607] ret_from_fork+0x10/0x20
> [ 0.114624] Code: 5280002b 1100054a b900092a f9800011 (885ffc01)
> [ 0.114631] ---[ end trace 0000000000000000 ]---
>
> Fixes: b81e3140e412 ("firmware: coreboot: Make bus registration symmetric")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Brian Norris <briannorris@chromium.org>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
> Currently, get_maintainers.pl tells me Greg should pick this up. But I
> CC the chrome-platform list too, since it seems reasonable for Google
> folks (probably ChromeOS folks are most active here?) to maintain
> Google/Chrome drivers.
>
> Let me know if y'all would like this official, and I'll push out a
> MAINTAINERS patch.
>

I think that would be a good idea.

Guenter

> drivers/firmware/google/coreboot_table.c | 37 +++++++++++++++++++-----
> 1 file changed, 29 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/firmware/google/coreboot_table.c b/drivers/firmware/google/coreboot_table.c
> index c52bcaa9def6..9ca21feb9d45 100644
> --- a/drivers/firmware/google/coreboot_table.c
> +++ b/drivers/firmware/google/coreboot_table.c
> @@ -149,12 +149,8 @@ static int coreboot_table_probe(struct platform_device *pdev)
> if (!ptr)
> return -ENOMEM;
>
> - ret = bus_register(&coreboot_bus_type);
> - if (!ret) {
> - ret = coreboot_table_populate(dev, ptr);
> - if (ret)
> - bus_unregister(&coreboot_bus_type);
> - }
> + ret = coreboot_table_populate(dev, ptr);
> +
> memunmap(ptr);
>
> return ret;
> @@ -169,7 +165,6 @@ static int __cb_dev_unregister(struct device *dev, void *dummy)
> static int coreboot_table_remove(struct platform_device *pdev)
> {
> bus_for_each_dev(&coreboot_bus_type, NULL, NULL, __cb_dev_unregister);
> - bus_unregister(&coreboot_bus_type);
> return 0;
> }
>
> @@ -199,6 +194,32 @@ static struct platform_driver coreboot_table_driver = {
> .of_match_table = of_match_ptr(coreboot_of_match),
> },
> };
> -module_platform_driver(coreboot_table_driver);
> +
> +static int __init coreboot_table_driver_init(void)
> +{
> + int ret;
> +
> + ret = bus_register(&coreboot_bus_type);
> + if (ret)
> + return ret;
> +
> + ret = platform_driver_register(&coreboot_table_driver);
> + if (ret) {
> + bus_unregister(&coreboot_bus_type);
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +static void __exit coreboot_table_driver_exit(void)
> +{
> + platform_driver_unregister(&coreboot_table_driver);
> + bus_unregister(&coreboot_bus_type);
> +}
> +
> +module_init(coreboot_table_driver_init);
> +module_exit(coreboot_table_driver_exit);
> +
> MODULE_AUTHOR("Google, Inc.");
> MODULE_LICENSE("GPL");

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