Re: [RFC/PATCH] x86: Use KERN_DEFAULT log-level in __show_regs()

From: Joe Perches
Date: Mon Dec 28 2009 - 14:47:42 EST


On Mon, 2009-12-28 at 10:26 +0200, Pekka Enberg wrote:
> From: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
>
> Andrew Morton reported a strange looking kmemcheck warning:
>
> WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (ffff88004fba6c20)
> 0000000000000000310000000000000000000000000000002413000000c9ffff
> u u u u u u u u u u u u u u u u i i i i i i i i u u u u u u u u
>
> [<ffffffff810af3aa>] kmemleak_scan+0x25a/0x540
> [<ffffffff810afbcb>] kmemleak_scan_thread+0x5b/0xe0
> [<ffffffff8104d0fe>] kthread+0x9e/0xb0
> [<ffffffff81003074>] kernel_thread_helper+0x4/0x10
> [<ffffffffffffffff>] 0xffffffffffffffff
>
> The above printout is missing register dump completely. The problem here is
> that the output comes from syslog which doesn't show KERN_INFO log-level
> messages. We didn't see this before because both of us were testing on 32-bit
> kernels which use the _default_ log-level.
>
> Fix that up by explicitly using KERN_DEFAULT log-level for __show_regs()
> printks.
>
> Cc: Vegard Nossum <vegard.nossum@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
> ---
> arch/x86/kernel/process.c | 4 ++--
> arch/x86/kernel/process_32.c | 14 +++++++-------
> arch/x86/kernel/process_64.c | 24 ++++++++++++------------
> 3 files changed, 21 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 98c2cde..c6ee241 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -103,8 +103,8 @@ void show_regs_common(void)
> if (!product)
> product = "";
>
> - printk("\n");
> - printk(KERN_INFO "Pid: %d, comm: %.20s %s %s %.*s %s/%s\n",
> + printk(KERN_CONT "\n");
> + printk(KERN_DEFAULT "Pid: %d, comm: %.20s %s %s %.*s %s/%s\n",

What is the reason to convert KERN_INFO to KERN_DEFAULT here?

The original commit for KERN_DEFAULT said:

This adds a KERN_DEFAULT loglevel marker, for when you cannot decide
which loglevel you want, and just want to keep an existing printk
with the default loglevel.

The difference between having KERN_DEFAULT and having no log-level
marker at all is two-fold:

- having the log-level marker will now force a new-line if the
previous printout had not added one (perhaps because it forgot,
but perhaps because it expected a continuation)

- having a log-level marker is required if you are printing out a
message that otherwise itself could perhaps otherwise be mistaken
for a log-level.


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