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. But it really doesn't matter (especially for arch/um). I will use the _irqsave variant for v4. I am OK with that. John Ogness
