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Date: Fri, 22 May 2020 11:38:23 +0100 From: Daniel Thompson <daniel.thompson@...aro.org> To: Sumit Garg <sumit.garg@...aro.org> Cc: kgdb-bugreport@...ts.sourceforge.net, jason.wessel@...driver.com, dianders@...omium.org, pmladek@...e.com, sergey.senozhatsky@...il.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH] kdb: Make kdb_printf robust to run in NMI context On Fri, May 22, 2020 at 03:32:26PM +0530, Sumit Garg wrote: > While rounding up CPUs via NMIs, its possible that a rounded up CPU > maybe holding a console port lock leading to kgdb master CPU stuck in > a deadlock during invocation of console write operations. So in order > to avoid such a deadlock, invoke bust_spinlocks() prior to invocation > of console handlers. > > Also, add a check for console port to be enabled prior to invocation of > corresponding handler. > > Suggested-by: Petr Mladek <pmladek@...e.com> > Suggested-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com> > Signed-off-by: Sumit Garg <sumit.garg@...aro.org> > --- > kernel/debug/kdb/kdb_io.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c > index 924bc92..e32ece6 100644 > --- a/kernel/debug/kdb/kdb_io.c > +++ b/kernel/debug/kdb/kdb_io.c > @@ -699,7 +699,11 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap) > } > } > for_each_console(c) { > + if (!(c->flags & CON_ENABLED)) > + continue; > + bust_spinlocks(1); > c->write(c, cp, retlen - (cp - kdb_buffer)); > + bust_spinlocks(0); I think it might actually be better to directly manipulate oops_in_progress here. bust_spinlocks(0) will call unblank_screen() and console_unblank() and I don't think calling these is worth the risk (and whilst kicking klogd is safe I think its also not required). Daniel. > touch_nmi_watchdog(); > } > } > @@ -761,7 +765,11 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap) > } > } > for_each_console(c) { > + if (!(c->flags & CON_ENABLED)) > + continue; > + bust_spinlocks(1); > c->write(c, moreprompt, strlen(moreprompt)); > + bust_spinlocks(0); > touch_nmi_watchdog(); > } > > -- > 2.7.4 >
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