Messages in this thread Patch in this message | | | From | John Ogness <> | Subject | [PATCH printk v2 09/11] panic: Add atomic write enforcement to oops | Date | Wed, 20 Sep 2023 01:14:54 +0206 |
| |
Invoke the atomic write enforcement functions for oops to ensure that the information gets out to the consoles.
Since there is no single general function that calls both oops_enter() and oops_exit(), the nesting feature of atomic write sections is taken advantage of in order to guarantee full coverage between the first oops_enter() and the last oops_exit().
It is important to note that if there are any legacy consoles registered, they will be attempting to directly print from the printk-caller context, which may jeopardize the reliability of the atomic consoles. Optimally there should be no legacy consoles registered.
Signed-off-by: John Ogness <john.ogness@linutronix.de> --- kernel/panic.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+)
diff --git a/kernel/panic.c b/kernel/panic.c index 86ed71ba8c4d..e2879098645d 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -614,6 +614,10 @@ bool oops_may_print(void) return pause_on_oops_flag == 0; } +static atomic_t oops_cpu = ATOMIC_INIT(-1); +static int oops_nesting; +static enum nbcon_prio oops_prev_prio; + /* * Called when the architecture enters its oops handler, before it prints * anything. If this is the first CPU to oops, and it's oopsing the first @@ -630,6 +634,36 @@ bool oops_may_print(void) */ void oops_enter(void) { + enum nbcon_prio prev_prio; + int cpu = -1; + + /* + * If this turns out to be the first CPU in oops, this is the + * beginning of the outermost atomic section. Otherwise it is + * the beginning of an inner atomic section. + */ + prev_prio = nbcon_atomic_enter(NBCON_PRIO_EMERGENCY); + + if (atomic_try_cmpxchg_relaxed(&oops_cpu, &cpu, smp_processor_id())) { + /* + * This is the first CPU in oops. Save the outermost + * @prev_prio in order to restore it on the outermost + * matching oops_exit(), when @oops_nesting == 0. + */ + oops_prev_prio = prev_prio; + + /* + * Enter an inner atomic section that ends at the end of this + * function. In this case, the nbcon_atomic_enter() above + * began the outermost atomic section. + */ + prev_prio = nbcon_atomic_enter(NBCON_PRIO_EMERGENCY); + } + + /* Track nesting when this CPU is the owner. */ + if (cpu == -1 || cpu == smp_processor_id()) + oops_nesting++; + tracing_off(); /* can't trust the integrity of the kernel anymore: */ debug_locks_off(); @@ -637,6 +671,9 @@ void oops_enter(void) if (sysctl_oops_all_cpu_backtrace) trigger_all_cpu_backtrace(); + + /* Exit inner atomic section. */ + nbcon_atomic_exit(NBCON_PRIO_EMERGENCY, prev_prio); } static void print_oops_end_marker(void) @@ -652,6 +689,18 @@ void oops_exit(void) { do_oops_enter_exit(); print_oops_end_marker(); + + if (atomic_read(&oops_cpu) == smp_processor_id()) { + oops_nesting--; + if (oops_nesting == 0) { + atomic_set(&oops_cpu, -1); + + /* Exit outmost atomic section. */ + nbcon_atomic_exit(NBCON_PRIO_EMERGENCY, oops_prev_prio); + } + } + put_cpu(); + kmsg_dump(KMSG_DUMP_OOPS); } -- 2.39.2
| |