On Fri, Feb 17, 2023 at 09:53:44AM +0106, John Ogness wrote: > The ttynull driver does not provide an implementation for the write() > callback. This leads to a NULL pointer dereference in the related > printing kthread, which assumes it can call that callback. > > Do not create kthreads for consoles that do not implement the write() > callback. Also, for pr_flush(), ignore consoles that do not implement > write() or write_atomic(), since there is no way those consoles can > flush their output. > > Link: https://lore.kernel.org/lkml/1831554214.546921.1676479103702.JavaMail.zimbra@xxxxxxx > Reported-by: Michael Thalmeier <michael.thalmeier@xxxxxxx> > Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx> Thank you! I will apply that to the next 5.10-rt build. Luis > --- > kernel/printk/printk.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index d2205872304d..64747c72fbea 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -2267,6 +2267,10 @@ static int printk_kthread_func(void *data) > /* Must be called within console_lock(). */ > static void start_printk_kthread(struct console *con) > { > + /* No need to start a printing thread if the console cannot print. */ > + if (!con->write) > + return; > + > con->thread = kthread_run(printk_kthread_func, con, > "pr/%s%d", con->name, con->index); > if (IS_ERR(con->thread)) { > @@ -3566,6 +3570,8 @@ bool pr_flush(int timeout_ms, bool reset_on_progress) > for_each_console(con) { > if (!(con->flags & CON_ENABLED)) > continue; > + if (!con->write && !con->write_atomic) > + continue; > printk_seq = atomic64_read(&con->printk_seq); > if (printk_seq < seq) > diff += seq - printk_seq; > -- > 2.30.2 > ---end quoted text---
