Re: [PATCH v2 0/9] Remove spin_unlock_wait()

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Jul 07, 2017 at 10:31:28AM +0200, Ingo Molnar wrote:
> Here's a quick list of all the use cases:
> 
>  net/netfilter/nf_conntrack_core.c:
> 
>    - This is I believe the 'original', historic spin_unlock_wait() usecase that
>      still exists in the kernel. spin_unlock_wait() is only used in a rare case, 
>      when the netfilter hash is resized via nf_conntrack_hash_resize() - which is 
>      a very heavy operation to begin with. It will no doubt get slower with the 
>      proposed changes, but it probably does not matter. A networking person 
>      Acked-by would be nice though.
> 
>  drivers/ata/libata-eh.c:
> 
>    - Locking of the ATA port in ata_scsi_cmd_error_handler(), presumably this can
>      race with IRQs and ioctls() on other CPUs. Very likely not performance 
>      sensitive in any fashion, on IO errors things stop for many seconds anyway.
> 
>  ipc/sem.c:
> 
>    - A rare race condition branch in the SysV IPC semaphore freeing code in 
>      exit_sem() - where even the main code flow is not performance sensitive, 
>      because typical database workloads get their semaphore arrays during startup 
>      and don't ever do heavy runtime allocation/freeing of them.
> 
>  kernel/sched/completion.c:
> 
>    - completion_done(). This is actually a (comparatively) rarely used completion 
>      API call - almost all the upstream usecases are in drivers, plus two in 
>      filesystems - neither usecase seems in a performance critical hot path. 
>      Completions typically involve scheduling and context switching, so in the 
>      worst case the proposed change adds overhead to a scheduling slow path.
> 

You missed the one in do_exit(), which I thought was the original one.