linux-kernel - Re: [PATCHv7 0/8] printk: use printk_safe to handle printk() recursive calls

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Message-ID: <20170105165847.GV14894@pathway.suse.cz>
Date:   Thu, 5 Jan 2017 17:58:47 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        Calvin Owens <calvinowens@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Hurley <peter@...leysoftware.com>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCHv7 0/8] printk: use printk_safe to handle printk()
 recursive calls

On Tue 2016-12-27 23:16:03, Sergey Senozhatsky wrote:
> Hello,
> 
> 	This patch set extends a lock-less NMI per-cpu buffers idea to
> handle recursive printk() calls. The basic mechanism is pretty much the
> same -- at the beginning of a deadlock-prone section we switch to lock-less
> printk callback, and return back to a default printk implementation at the
> end; the messages are getting flushed to a logbuf buffer from a safer
> context.
> 
> See patch 0006 for examples of possible deadlock scenarios that are
> handled by printk-safe.
> 
> 
> v7:
> -- don't touch printk_nmi_enter/exit
> -- new printk_safe macros naming: printk_safe_enter_irqsave/exit_irqrestore
> -- added printk_safe_enter_irq/printk_safe_exit_irq
> -- added patch that converts the rest of printk.c to printk-safe
> -- fix build error on !NMI configs
> -- improved lost_messages reporting
> 
> v6:
> -- re-based
> -- addressed Petr's review (added comments; moved lost accounting to seq buf)
> ...
> 
> [against next-20161224 + "printk: always report dropped messages" patch set]
> 
> Sergey Senozhatsky (8):
>   printk: use vprintk_func in vprintk()
>   printk: rename nmi.c and exported api
>   printk: introduce per-cpu safe_print seq buffer
>   printk: always use deferred printk when flush printk_safe lines
>   printk: report lost messages in printk safe/nmi contexts
>   printk: use printk_safe buffers in printk
>   printk: remove zap_locks() function
>   printk: convert the rest to printk-safe
> 
>  include/linux/printk.h                 |  21 ++-
>  init/Kconfig                           |  16 ++-
>  init/main.c                            |   2 +-
>  kernel/kexec_core.c                    |   2 +-
>  kernel/panic.c                         |   4 +-
>  kernel/printk/Makefile                 |   2 +-
>  kernel/printk/internal.h               |  79 ++++++-----
>  kernel/printk/printk.c                 | 220 +++++++++++++------------------
>  kernel/printk/{nmi.c => printk_safe.c} | 234 +++++++++++++++++++++++----------
>  lib/nmi_backtrace.c                    |   2 +-
>  10 files changed, 335 insertions(+), 247 deletions(-)
>  rename kernel/printk/{nmi.c => printk_safe.c} (53%)

The entire patchset looks fine from my point of view.

Andrew, if you do not mind, I am going to make it tested in linux-next
via mine new git tree, see
https://git.kernel.org/cgit/linux/kernel/git/pmladek/printk.git/

I will push there also the patch that modifies MAINTAINERS file.
Then I will try to get all these changes upstream in the next merge
window.

It will be great if you still could keep an eye over the printk
patches and stop us when we do something bad.

Best Regards,
Petr