Re: [PATCH v6 0/5] Handle NBCON consoles on KDB

[Petr Mladek <pmladek@suse.com>]

On Thu 2025-10-16 11:47:53, Marcos Paulo de Souza wrote:
> In v6 the patches were rebased on top of v6.18-rc1, added Reviewed-by tags from
> John and did some small changes suggested by him as well.
> 
> As usual, how I tested the changes:
> 
> Testing
> -------
> 
> I did the tests using qemu and reapplying commit f79b163c4231
> ('Revert "serial: 8250: Switch to nbcon console"') created originally by
> John, just to exercise the common 8250 serial from qemu. The commit can
> be checked on [1]. I had to solve some conflicts since the code has been
> reworked after the commit was reverted.
> 
> Then I would create three different serial entries on qemu:
> -serial mon:stdio -serial pty -serial pty
> 
> And for the kernel command line I added:
> earlyprintk=serial,ttyS2 console=ttyS2 console=ttyS1 console=ttyS1 kgdboc=ttyS1,115200
> 
> Without the last patch on this patchset, when KDB is triggered, the mirroring
> only worked on the earlyprintk console, since it's using the legacy console.
> 
> With the last patch applied, KDB mirroring works on legacy and nbcon
> console. For debugging I added some messages to be printed by KDB, showing
> also the console->name and console->index, and I was able to see both
> ->write and ->write_atomic being called, and it all working together.
> 
> [1]: https://github.com/marcosps/linux/commit/618bd49f8533db85d9c322f9ad1cb0da22aca9ee
> [2]: https://lore.kernel.org/lkml/20250825022947.1596226-1-wangjinchao600@gmail.com/
> 
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
> ---
> Changes in v6:
> - Rebased on top opf v6.18-rc1
> - Changed some includes, as suggedted by John
> - Reworked comments as suggested by John
> 
> Changes in v5:
> - Added review tags from Petr
> - Changes the way we detect if a CPU is running KDB.
> - Link to v4: https://lore.kernel.org/r/20250915-nbcon-kgdboc-v4-0-e2b6753bb566@suse.com
> 
> Changes in v4:
> - Added ifdefs to only check for KGDB if KGDB was enabled, suggested by John Ogness
> - Updated comments about KDB on acquire_direct, suggested by Petr and John
> - Added a new patch to export nbcon_write_context_set_buf, suggested by Petr and John
> - Link to v3: https://lore.kernel.org/r/20250902-nbcon-kgdboc-v3-0-cd30a8106f1c@suse.com
> 
> Changes in v3:
> - Only call nbcon_context_release if nbcon_context_exit_unsafe returns true (John Ogness)
> - Dropped the prototype of console_is_usable from kernel/printk/internal. (Petr Mladek)
> - Add comments to the new functions introduced (Petr Mladek)
> - Flush KDB console on nbcon_kdb_release (Petr Mladek)
> - Add an exception for KDB on nbcon_context_try_acquire_direct (John Ogness and Petr Mladek)
> - Link to v2: https://lore.kernel.org/r/20250811-nbcon-kgdboc-v2-0-c7c72bcdeaf6@suse.com
> 
> Changes in v2:
> - Set by mistake ..
> - Link to v1: https://lore.kernel.org/r/20250713-nbcon-kgdboc-v1-0-51eccd9247a8@suse.com
> 
> ---
> Marcos Paulo de Souza (5):
>       printk: nbcon: Export console_is_usable
>       printk: nbcon: Introduce KDB helpers
>       printk: nbcon: Allow KDB to acquire the NBCON context
>       printk: nbcon: Export nbcon_write_context_set_buf
>       kdb: Adapt kdb_msg_write to work with NBCON consoles
> 
>  include/linux/console.h   | 55 ++++++++++++++++++++++++++++++++++++
>  include/linux/kdb.h       | 16 +++++++++++
>  kernel/debug/kdb/kdb_io.c | 47 +++++++++++++++++++++----------
>  kernel/printk/internal.h  | 45 ------------------------------
>  kernel/printk/nbcon.c     | 71 +++++++++++++++++++++++++++++++++++++++++++++--
>  5 files changed, 171 insertions(+), 63 deletions(-)

With the two below compilation fixes, the series seems to be ready for
linux-next.

I am going to wait with pushing a week or so to give other printk and
kdb maintainers and reviewers a chance to look at it.

The following two changes are needed to fix build with
CONFIG_PRINTK and/or CONFIG_KGDB_KDB disabled. I am going
to do the in the respective patches when committing:

diff --git a/include/linux/console.h b/include/linux/console.h
index 81d2c247c01f..690a5f698a5c 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -664,7 +664,7 @@ static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return
 static inline void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) { }
 static inline bool nbcon_kdb_try_acquire(struct console *con,
 					 struct nbcon_write_context *wctxt) { return false; }
-static inline void nbcon_kdb_release(struct console *con) { }
+static inline void nbcon_kdb_release(struct nbcon_write_context *wctxt) { }
 static inline bool console_is_usable(struct console *con, short flags,
 				     bool use_atomic) { return false; }
 #endif
diff --git a/include/linux/kdb.h b/include/linux/kdb.h
index db9d73b12a1a..741c58e86431 100644
--- a/include/linux/kdb.h
+++ b/include/linux/kdb.h
@@ -226,7 +226,7 @@ static inline void kdb_init(int level) {}
 static inline int kdb_register(kdbtab_t *cmd) { return 0; }
 static inline void kdb_unregister(kdbtab_t *cmd) {}
 
-static inline bool kdb_printf_on_this_cpu(void) { return false };
+static inline bool kdb_printf_on_this_cpu(void) { return false; }
 
 #endif	/* CONFIG_KGDB_KDB */
 enum {


Best Regards,
Petr




> ---
> base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
> change-id: 20250713-nbcon-kgdboc-efcfc37fde46
> 
> Best regards,
> --  
> Marcos Paulo de Souza <mpdesouza@suse.com>