Messages in this thread Patch in this message |  | | Date | Sat, 18 Jul 2020 14:10:53 +0200 | From | Marco Elver <> | Subject | Re: [PATCH v5 4/4] printk: use the lockless ringbuffer |
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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();
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