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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: b81e3140e4 ("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>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20221019180934.1.If29e167d8a4771b0bf4a39c89c6946ed764817b9@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.