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SubjectRe: [PATCH v2] sysrq: Use panic() to force a crash
On Thu, Sep 20, 2018 at 10:12:53AM -0700, Matthias Kaehlcke wrote:
> sysrq_handle_crash() currently forces a crash by dereferencing a
> NULL pointer, which is undefined behavior in C. Just call panic()
> instead, which is simpler and doesn't depend on compiler specific
> handling of the undefined behavior.
>
> Remove the comment on why the RCU lock needs to be released, it isn't
> accurate anymore since the crash now isn't handled by the page fault
> handler (for reference: the comment was added by commit 984cf355aeaa
> ("sysrq: Fix warning in sysrq generated crash.")). Releasing the lock
> is still good practice though.
>
> Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
> drivers/tty/sysrq.c | 13 +++----------
> 1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index 06ed20dd01ba..d779a51499a0 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -134,17 +134,10 @@ static struct sysrq_key_op sysrq_unraw_op = {
>
> static void sysrq_handle_crash(int key)
> {
> - char *killer = NULL;
> -
> - /* we need to release the RCU read lock here,
> - * otherwise we get an annoying
> - * 'BUG: sleeping function called from invalid context'
> - * complaint from the kernel before the panic.
> - */
> + /* release the RCU read lock before crashing */
> rcu_read_unlock();
> - panic_on_oops = 1; /* force panic */
> - wmb();
> - *killer = 1;
> +
> + panic("sysrq triggered crash\n");
> }
> static struct sysrq_key_op sysrq_crash_op = {
> .handler = sysrq_handle_crash,

Does this need further changes or is it ready to land?

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