Messages in this thread | | | Date | Wed, 4 Mar 2020 16:21:59 +0100 | From | Petr Mladek <> | Subject | Re: [PATCHv2] printk: queue wake_up_klogd irq_work only if per-CPU areas are ready |
| |
On Tue 2020-03-03 20:30:02, Sergey Senozhatsky wrote: > However, only printk_safe/printk_nmi do make sure that > per-CPU areas have been initialised and that it's safe > to modify per-CPU irq_work. This means that, for instance, > should printk_deferred() be invoked "too early", that > is before per-CPU areas are initialised, printk_deferred() > will perform illegal per-CPU access. > > Lech Perczak [0] reports that after commit 1b710b1b10ef > ("char/random: silence a lockdep splat with printk()") > user-space syslog/kmsg readers are not able to read new > kernel messages. The reason is printk_deferred() being > called too early (as was pointed out by Petr and John). > > Fix printk_deferred() and do not queue per-CPU irq_work > before per-CPU areas are initialized. > > [0] https://lore.kernel.org/lkml/aa0732c6-5c4e-8a8b-a1c1-75ebe3dca05b@camlintechnologies.com/ > > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> > Reported-by: Lech Perczak <l.perczak@camlintechnologies.com> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Theodore Ts'o <tytso@mit.edu> > Cc: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Now, the question is whether to hurry this fix into 5.6 or if it could wait for 5.7.
I think that it could wait because 5.6 is not affected by the particular printk_deferred(). This patch fixes a long-term generic problem. But I am open for other opinions.
Best Regards, Petr
| |