On Tue 2021-03-02 09:06:07, John Ogness wrote: > On 2021-03-01, Petr Mladek <[email protected]> wrote: > >> > diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c > >> > index 6516ef1f8274..4869e2cc787c 100644 > >> > --- a/arch/um/kernel/kmsg_dump.c > >> > +++ b/arch/um/kernel/kmsg_dump.c > >> > @@ -1,5 +1,6 @@ > >> > // SPDX-License-Identifier: GPL-2.0 > >> > #include <linux/kmsg_dump.h> > >> > +#include <linux/spinlock.h> > >> > #include <linux/console.h> > >> > #include <linux/string.h> > >> > #include <shared/init.h> > >> > @@ -9,6 +10,7 @@ > >> > static void kmsg_dumper_stdout(struct kmsg_dumper *dumper, > >> > enum kmsg_dump_reason reason) > >> > { > >> > + static DEFINE_SPINLOCK(lock); > >> > static char line[1024]; > >> > struct console *con; > >> > size_t len = 0; > >> > @@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper > >> > *dumper, > >> > if (con) > >> > return; > >> > > >> > + if (!spin_trylock(&lock)) > >> > >> I have almost missed this. It is wrong. The last version correctly > >> used > >> > >> if (!spin_trylock_irqsave(&lock, flags)) > >> > >> kmsg_dump(KMSG_DUMP_PANIC) is called in panic() with interrupts > >> disabled. We have to store the flags here. > > > > Ah, I get always confused with these things. spin_trylock() can > > actually get called in a context with IRQ disabled. So it is not > > as wrong as I thought. > > > > But still. panic() and kmsg_dump() can be called in IRQ context. > > So, this function might be called in IRQ context. So, it feels > > more correct to use the _irqsafe variant here. > > > > I know that there is the trylock so it probably does not matter much. > > Well, the disabled irq might help to serialize the two calls when > > one is in normal context and the other would happen in IRQ one. > > > > As I said, using _irqsafe variant looks better to me. > > For the record, the reason I removed the _irqsave for v3 is because I > felt like it was misleading, appearing to be necessary when it is not. > > I think anyone could argue both sides.
Yeah, I could imagine myself to have different opinion another day or year. I am sorry for the noise. > But it really doesn't matter > (especially for arch/um). I will use the _irqsave variant for v4. I am > OK with that. Please do, if it is easy. You are going to send v4 anyway. Best Regards, Petr
