Re: [PATCH 1/5] mm: hide laptop_mode_wb_timer entirely behind the BDI API

[Guenter Roeck <linux@roeck-us.net>]

On Mon, Aug 09, 2021 at 04:17:40PM +0200, Christoph Hellwig wrote:
> Don't leak the detaÑ–ls of the timer into the block layer, instead
> initialize the timer in bdi_alloc and delete it in bdi_unregister.
> Note that this means the timer is initialized (but not armed) for
> non-block queues as well now.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---

Just in case this hasn't been reported yet.
This patch results in a widespread build failure. Example:

Building x86_64:tinyconfig ... failed
--------------
Error log:
mm/page-writeback.c:2044:6: error: redefinition of 'laptop_sync_completion'
 2044 | void laptop_sync_completion(void)
      |      ^~~~~~~~~~~~~~~~~~~~~~
In file included from include/linux/memcontrol.h:22,
                 from include/linux/swap.h:9,
                 from mm/page-writeback.c:20:
include/linux/writeback.h:345:20: note: previous definition of 'laptop_sync_completion' with type 'void(void)'
  345 | static inline void laptop_sync_completion(void) { }
      |                    ^~~~~~~~~~~~~~~~~~~~~~
make[2]: *** [scripts/Makefile.build:272: mm/page-writeback.o] Error 1

Guenter

---
bisect log:

# bad: [92d00774360dfd4151f15ab9905c643347b9f242] Add linux-next specific files for 20210810
# good: [36a21d51725af2ce0700c6ebcb6b9594aac658a6] Linux 5.14-rc5
git bisect start 'HEAD' 'v5.14-rc5'
# good: [01dda625c9b7cfd3bf5ac05f73da8c512792f94c] Merge remote-tracking branch 'crypto/master'
git bisect good 01dda625c9b7cfd3bf5ac05f73da8c512792f94c
# bad: [75cadd49361c6650764d35bcbb6c9cb9f0a9d9a3] Merge remote-tracking branch 'irqchip/irq/irqchip-next'
git bisect bad 75cadd49361c6650764d35bcbb6c9cb9f0a9d9a3
# good: [511b0c991c9d49fd6d8188f799b10aa0465cecf3] Merge remote-tracking branch 'drm-intel/for-linux-next'
git bisect good 511b0c991c9d49fd6d8188f799b10aa0465cecf3
# good: [f3b48aa06fb8b4384b90e41220da8be5a4013a6d] Merge remote-tracking branch 'input/next'
git bisect good f3b48aa06fb8b4384b90e41220da8be5a4013a6d
# bad: [87470038c43f9577a300a29ba6c2c95d28039464] Merge remote-tracking branch 'regulator/for-next'
git bisect bad 87470038c43f9577a300a29ba6c2c95d28039464
# bad: [e1796683109e4ba27c73f099486555a36820b175] Merge remote-tracking branch 'device-mapper/for-next'
git bisect bad e1796683109e4ba27c73f099486555a36820b175
# bad: [a11d7fc2d05fb509cd9e33d4093507d6eda3ad53] block: remove the bd_bdi in struct block_device
git bisect bad a11d7fc2d05fb509cd9e33d4093507d6eda3ad53
# good: [a291bb43e5c9fdedc4be3dfd496e64e7c5a78b1f] block: use the %pg format specifier in show_partition
git bisect good a291bb43e5c9fdedc4be3dfd496e64e7c5a78b1f
# good: [2112f5c1330a671fa852051d85cb9eadc05d7eb7] loop: Select I/O scheduler 'none' from inside add_disk()
git bisect good 2112f5c1330a671fa852051d85cb9eadc05d7eb7
# good: [ba30585936b0b88f0fb2b19be279b346a6cc87eb] dm: move setting md->type into dm_setup_md_queue
git bisect good ba30585936b0b88f0fb2b19be279b346a6cc87eb
# bad: [5ed964f8e54eb3191b8b7b45aeb52672a0c995dc] mm: hide laptop_mode_wb_timer entirely behind the BDI API
git bisect bad 5ed964f8e54eb3191b8b7b45aeb52672a0c995dc
# good: [d1254a8749711e0d7441036a74ce592341f89697] block: remove support for delayed queue registrations
git bisect good d1254a8749711e0d7441036a74ce592341f89697
# first bad commit: [5ed964f8e54eb3191b8b7b45aeb52672a0c995dc] mm: hide laptop_mode_wb_timer entirely behind the BDI API