Messages in this thread | | | From | Sumit Garg <> | Date | Tue, 2 Jun 2020 19:32:46 +0530 | Subject | Re: [PATCH v4 4/4] kdb: Switch to use safer dbg_io_ops over console APIs |
| |
On Tue, 2 Jun 2020 at 19:16, Daniel Thompson <daniel.thompson@linaro.org> wrote: > > 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.thompson@linaro.org> > > Signed-off-by: Sumit Garg <sumit.garg@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. >
Okay, will update it in the next version.
-Sumit
> > Daniel.
| |