Re: [PATCH] fgraph: Still initialize idle shadow stacks when starting

[Steven Rostedt]

On December 12, 2024 3:49:37 PM EST, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
>On Wed, Dec 11, 2024 at 7:53 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
>> From: Steven Rostedt <rostedt@xxxxxxxxxxx>
>>
>> A bug was discovered where the idle shadow stacks were not initialized
>> for offline CPUs when starting function graph tracer, and when they came
>> online they were not traced due to the missing shadow stack. To fix
>> this, the idle task shadow stack initialization was moved to using the
>> CPU hotplug callbacks. But it removed the initialization when the
>> function graph was enabled. The problem here is that the hotplug
>> callbacks are called when the CPUs come online, but the idle shadow
>> stack initialization only happens if function graph is currently
>> active. This caused the online CPUs to not get their shadow stack
>> initialized.
>>
>> The idle shadow stack initialization still needs to be done when the
>> function graph is registered, as they will not be allocated if function
>> graph is not registered.
>>
>> Cc: stable@xxxxxxxxxxxxxxx
>> Fixes: 2c02f7375e65 ("fgraph: Use CPU hotplug mechanism to initialize idle shadow stacks")
>> Reported-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
>> Closes: https://lore.kernel.org/all/CACRpkdaTBrHwRbbrphVy-=SeDz6MSsXhTKypOtLrTQ+DgGAOcQ@xxxxxxxxxxxxxx/
>> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
>
>Yep that solves my issue and I can go on debugging my boot!
>Tested-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
>
>Thanks for patching this up so quickly Stephen, you're the best.
>

No problem, but I don't know who this "Stephen" is? ;-)

-- Steve

>Yours,
>Linus Walleij