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Subject[PATCH] firmware: coreboot: Register bus in module init
Date
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>
---
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.

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");
--
2.38.0.413.g74048e4d9e-goog
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