On Fri, May 29, 2020 at 04:56:47PM +0530, 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. > > Suggested-by: Daniel Thompson <daniel.thomp...@linaro.org> > Signed-off-by: Sumit Garg <sumit.g...@linaro.org>
Looking good, only one minor comment left on my side (including the three patches prior). > diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c > index 9e5a40d..5e00bc8 100644 > --- a/kernel/debug/kdb/kdb_io.c > +++ b/kernel/debug/kdb/kdb_io.c > @@ -560,12 +560,14 @@ static void kdb_msg_write(char *msg, int msg_len) > if (msg_len == 0) > return; > > - if (dbg_io_ops && !dbg_io_ops->is_console) > + if (dbg_io_ops) > kdb_io_write(msg, msg_len); Since this now slots on so cleanly and there are not multiple calls to kdb_io_write() then I think perhaps factoring this out into its own function (in patch 1) is no long necessary. The character write loop can go directly into this function. Daniel.
