lkml.org 
[lkml]   [2020]   [Jul]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH v5 4/4] printk: use the lockless ringbuffer
On Thu, Jul 09, 2020 at 03:29PM +0206, John Ogness wrote:
> Replace the existing ringbuffer usage and implementation with
> lockless ringbuffer usage. Even though the new ringbuffer does not
> require locking, all existing locking is left in place. Therefore,
> this change is purely replacing the underlining ringbuffer.
>
> Changes that exist due to the ringbuffer replacement:
>
> - The VMCOREINFO has been updated for the new structures.
>
> - Dictionary data is now stored in a separate data buffer from the
> human-readable messages. The dictionary data buffer is set to the
> same size as the message buffer. Therefore, the total required
> memory for both dictionary and message data is
> 2 * (2 ^ CONFIG_LOG_BUF_SHIFT) for the initial static buffers and
> 2 * log_buf_len (the kernel parameter) for the dynamic buffers.
>
> - Record meta-data is now stored in a separate array of descriptors.
> This is an additional 72 * (2 ^ (CONFIG_LOG_BUF_SHIFT - 5)) bytes
> for the static array and 72 * (log_buf_len >> 5) bytes for the
> dynamic array.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Petr Mladek <pmladek@suse.com>

It seems this causes a regression observed at least with newline-only
printks. I noticed this during -next testing because various debugging
tools (K*SAN, lockdep, etc.) use e.g. pr_{err,warn,info}("\n") to format
reports.

Without wanting to wait for a report from one of these debugging tools,
a simple reproducer is below. Without this patch, the expected newline
is printed.

Thanks,
-- Marco

------ >8 ------

--- a/init/main.c
+++ b/init/main.c
@@ -1039,6 +1039,10 @@ asmlinkage __visible void __init start_kernel(void)
sfi_init_late();
kcsan_init();

+ pr_info("EXPECT BLANK LINE --vv\n");
+ pr_info("\n");
+ pr_info("EXPECT BLANK LINE --^^\n");
+
/* Do the rest non-__init'ed, we're now alive */
arch_call_rest_init();

\
 
 \ /
  Last update: 2020-07-18 14:11    [W:0.515 / U:1.384 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site