[ Andrew, can you pull this patch into -mm? ]
As I was testing a lot of my code recently, and having several
"successes", I accidentally noticed in the dmesg this little line:
[ 0.000000] start_kernel(): bug: interrupts were enabled *very* early,
fixing it
Sure enough, one of my patches two commits ago enabled interrupts early.
The sad part here is that I never noticed it, and I ran several tests
with ktest too, and ktest did not notice this line.
What ktest looks for (and so does many other automated testing scripts)
is a back trace produced by a WARN_ON() or BUG(). As a back trace was
never produced, my buggy patch could have slipped into linux-next, or
even worse, mainline.
Adding a WARN(!irqs_disabled()) makes this bug a little more obvious:
[ 0.000000] PID hash table entries: 4096 (order: 3, 32768 bytes)
[ 0.000000] __ex_table already sorted, skipping sort
[ 0.000000] Checking aperture...
[ 0.000000] No AGP bridge found
[ 0.000000] Calgary: detecting Calgary via BIOS EBDA area
[ 0.000000] Calgary: Unable to locate Rio Grande table in EBDA - bailing!
[ 0.000000] Memory: 2003252k/2054848k available (4857k kernel code, 460k
absent, 51136k reserved, 6210k data, 1096k init)
[ 0.000000] ------------[ cut here ]------------
[ 0.000000] WARNING: at
/home/rostedt/work/git/linux-trace.git/init/main.c:543
start_kernel+0x21e/0x415()
[ 0.000000] Hardware name: To Be Filled By O.E.M.
[ 0.000000] Interrupts were enabled *very* early, fixing it
[ 0.000000] Modules linked in:
[ 0.000000] Pid: 0, comm: swapper/0 Not tainted 3.8.0-test+ #286
[ 0.000000] Call Trace:
[ 0.000000] [<ffffffff81037b79>] warn_slowpath_common+0x83/0x9b
[ 0.000000] [<ffffffff81037c34>] warn_slowpath_fmt+0x46/0x48
[ 0.000000] [<ffffffff81ae4a39>] start_kernel+0x21e/0x415
[ 0.000000] [<ffffffff81ae4623>] ? repair_env_string+0x56/0x56
[ 0.000000] [<ffffffff81ae4312>] x86_64_start_reservations+0x10e/0x112
[ 0.000000] [<ffffffff81ae4120>] ? early_idt_handlers+0x120/0x120
[ 0.000000] [<ffffffff81ae4418>] x86_64_start_kernel+0x102/0x111
[ 0.000000] ---[ end trace 007d8b0491b4f5d8 ]---
[ 0.000000] Preemptible hierarchical RCU implementation.
[ 0.000000] RCU restricting CPUs from NR_CPUS=8 to nr_cpu_ids=4.
[ 0.000000] NR_IRQS:4352 nr_irqs:712 16
[ 0.000000] Console: colour VGA+ 80x25
[ 0.000000] console [ttyS0] enabled, bootconsole disabled
Do you see it?
The original version of this patch just slapped a WARN_ON() in there and
kept the printk(). Ard van Breemen suggested using the WARN() interface,
which makes the code a bit cleaner.
Also, while examining other warnings in init/main.c, I found two other
locations that deserve a bloody murder scream if their conditions are
hit, and updated them accordingly.
Cc: Ard van Breemen <a...@telegraafnet.nl>
Signed-off-by: Steven Rostedt <rost...@goodmis.org>
Index: linux-trace.git/init/main.c
===================================================================
--- linux-trace.git.orig/init/main.c
+++ linux-trace.git/init/main.c
@@ -539,11 +539,8 @@ asmlinkage void __init start_kernel(void
* fragile until we cpu_idle() for the first time.
*/
preempt_disable();
- if (!irqs_disabled()) {
- printk(KERN_WARNING "start_kernel(): bug: interrupts were "
- "enabled *very* early, fixing it\n");
+ if (WARN(!irqs_disabled(), "Interrupts were enabled *very* early,
fixing it\n"))
local_irq_disable();
- }
idr_init_cache();
perf_event_init();
rcu_init();
@@ -558,9 +555,7 @@ asmlinkage void __init start_kernel(void
time_init();
profile_init();
call_function_init();
- if (!irqs_disabled())
- printk(KERN_CRIT "start_kernel(): bug: interrupts were "
- "enabled early\n");
+ WARN(!irqs_disabled(), "Interrupts were enabled early\n");
early_boot_irqs_disabled = false;
local_irq_enable();
@@ -702,9 +697,7 @@ int __init_or_module do_one_initcall(ini
strlcat(msgbuf, "disabled interrupts ", sizeof(msgbuf));
local_irq_enable();
}
- if (msgbuf[0]) {
- printk("initcall %pF returned with %s\n", fn, msgbuf);
- }
+ WARN(msgbuf[0], "initcall %pF returned with %s\n", fn, msgbuf);
return ret;
}
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