On Tue 2019-04-23 15:25:11, Sergey Senozhatsky wrote: > We need to take console_sem lock when we iterate console > drivers list. Otherwise, another CPU can concurrently > modify console drivers list or console drivers. > > Signed-off-by: Sergey Senozhatsky <[email protected]> > --- > kernel/printk/printk.c | 19 +++++++++++++------ > 1 file changed, 13 insertions(+), 6 deletions(-) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index b0e361ca1bea..c2bccf58d03e 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -2674,12 +2674,17 @@ void register_console(struct console *newcon) > struct console_cmdline *c; > static bool has_preferred; > > - if (console_drivers) > - for_each_console(bcon) > - if (WARN(bcon == newcon, > - "console '%s%d' already registered\n", > - bcon->name, bcon->index)) > - return; > + console_lock(); > + if (console_drivers) { > + for_each_console(bcon) { > + if (bcon != newcon) > + continue; > + WARN(1, "console '%s%d' already registered\n", > + bcon->name, bcon->index); > + console_unlock(); > + return; > + } > + } > > /* > * before we register a new CON_BOOT console, make sure we don't > @@ -2691,6 +2696,7 @@ void register_console(struct console *newcon) > if (!(bcon->flags & CON_BOOT)) { > pr_info("Too late to register bootconsole > %s%d\n", > newcon->name, newcon->index); > + console_unlock(); > return; > } > } > @@ -2701,6 +2707,7 @@ void register_console(struct console *newcon) > > if (!has_preferred || bcon || !console_drivers) > has_preferred = preferred_console >= 0; > + console_unlock();
We should keep it until the console is added into the list. Otherwise there are races with accessing the static has_preferred and the global preferred_console variables. Also the value of bcon should stay synchronized until we decide about replaying the log. IMHO, the only danger might be when con->match() or con->setup() would want to take console_lock() as well. I checked few drivers and they looked safe. But I did not check all of them. What do you think, please? Best Regards, Petr
