Re: [PATCH/RFC v5 4/5]: core: Add dump device to call on oopses and panics

Artem Bityutskiy
2009-11-30T08:52:45Z

On Mon, 2009-11-30 at 08:46 +0100, Jörn Engel wrote:
> On Mon, 30 November 2009 09:27:51 +0200, Artem Bityutskiy wrote:
> >
> > To me it looks like 'log_end' is not supposed to wrap. What makes you
> > think it can? In which cases it can?
>
> It is a 32bit variable. Would do you expect happens once you reach
> 0xffffffff and add 1?

Yes, now I see log_end is an ever increasing variable.

How about this patch on top of the existing one (untested):

diff --git a/kernel/printk.c b/kernel/printk.c
index f711b99..66995ca 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1486,28 +1486,27 @@ static const char *kmsg_to_str(enum kmsg_dump_reason reason)
*/
void kmsg_dump(enum kmsg_dump_reason reason)
{
- unsigned long len = ACCESS_ONCE(log_end);
+ unsigned long end = ACCESS_ONCE(log_end) & LOG_BUF_MASK;
struct kmsg_dumper *dumper;
const char *s1, *s2;
unsigned long l1, l2;
unsigned long flags;

- s1 = "";
- l1 = 0;
- s2 = log_buf;
- l2 = len;
-
- /* Have we rotated around the circular buffer? */
- if (len > log_buf_len) {
- unsigned long pos = len & LOG_BUF_MASK;
-
- s1 = log_buf + pos;
- l1 = log_buf_len - pos;
-
- s2 = log_buf;
- l2 = pos;
+ /*
+ * Have we ever rotated around the circular buffer? If we never did,
+ * we have to have zeroes at the end.
+ */
+ if (log_buf[end]) {
+ s1 = log_buf + end;
+ l1 = log_buf_len - end;
+ } else {
+ s1 = "";
+ l1 = 0;
}

+ s2 = log_buf;
+ l2 = end;
+
if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
kmsg_to_str(reason));

Then the whole function will look like this:

/**
* kmsg_dump - dump kernel log to kernel message dumpers.
* @reason: the reason (oops, panic etc) for dumping
*
* Iterate through each of the dump devices and call the oops/panic
* callbacks with the log buffer.
*/
void kmsg_dump(enum kmsg_dump_reason reason)
{
unsigned long end = ACCESS_ONCE(log_end) & LOG_BUF_MASK;
struct kmsg_dumper *dumper;
const char *s1, *s2;
unsigned long l1, l2;
unsigned long flags;

/*
* Have we ever rotated around the circular buffer? If we never did,
* we have to have zeroes at the end.
*/
if (log_buf[end]) {
s1 = log_buf + end;
l1 = log_buf_len - end;
} else {
s1 = "";
l1 = 0;
}

s2 = log_buf;
l2 = end;

if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
kmsg_to_str(reason));
return;
}
list_for_each_entry(dumper, &dump_list, list)
dumper->dump(dumper, reason, s1, l1, s2, l2);
spin_unlock_irqrestore(&dump_list_lock, flags);
}

--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)