On Wed 2020-06-03 12:52:15, Sumit Garg wrote: > In kgdb context, calling console handlers aren't safe due to locks used > in those handlers which could in turn lead to a deadlock. Although, using > oops_in_progress increases the chance to bypass locks in most console > handlers but it might not be sufficient enough in case a console uses > more locks (VT/TTY is good example). > > Currently when a driver provides both polling I/O and a console then kdb > will output using the console. We can increase robustness by using the > currently active polling I/O driver (which should be lockless) instead > of the corresponding console. For several common cases (e.g. an > embedded system with a single serial port that is used both for console > output and debugger I/O) this will result in no console handler being > used. > > In order to achieve this we need to reverse the order of preference to > use dbg_io_ops (uses polling I/O mode) over console APIs. So we just > store "struct console" that represents debugger I/O in dbg_io_ops and > while emitting kdb messages, skip console that matches dbg_io_ops > console in order to avoid duplicate messages. After this change, > "is_console" param becomes redundant and hence removed. > > diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c > index 4139698..6e182aa 100644 > --- a/drivers/tty/serial/kgdboc.c > +++ b/drivers/tty/serial/kgdboc.c > @@ -558,6 +557,7 @@ static int __init kgdboc_earlycon_init(char *opt) > } > > earlycon = con; > + kgdboc_earlycon_io_ops.cons = con; > pr_info("Going to register kgdb with earlycon '%s'\n", con->name); > if (kgdb_register_io_module(&kgdboc_earlycon_io_ops) != 0) { > earlycon = NULL;
Should we clear kgdboc_earlycon_io_ops.cons here when kgdb_register_io_module() failed? > diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h > index c62d764..529116b 100644 > --- a/include/linux/kgdb.h > +++ b/include/linux/kgdb.h > @@ -276,8 +276,7 @@ struct kgdb_arch { > * the I/O driver. > * @post_exception: Pointer to a function that will do any cleanup work > * for the I/O driver. > - * @is_console: 1 if the end device is a console 0 if the I/O device is > - * not a console > + * @cons: valid if the I/O device is a console; else NULL. > */ > struct kgdb_io { > const char *name; > @@ -288,7 +287,7 @@ struct kgdb_io { > void (*deinit) (void); > void (*pre_exception) (void); > void (*post_exception) (void); > - int is_console; > + struct console *cons; Nit: I would call it "con". The trailing 's' makes me feel that that the variable points to an array or list of consoles. > }; > Otherwise, it looks pretty straightforward. Best Regards, Petr