Re: [patch 08/10] kernel/locking/lockdep.c: convert hash tables to hlists

[Ingo Molnar]

* akpm@xxxxxxxxxxxxxxxxxxxx <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:

> From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Subject: kernel/locking/lockdep.c: convert hash tables to hlists
> 
> Mike said:
> 
> : CONFIG_UBSAN_ALIGNMENT breaks x86-64 kernel with lockdep enabled, i.  e
> : kernel with CONFIG_UBSAN_ALIGNMENT fails to load without even any error
> : message.
> : 
> : The problem is that ubsan callbacks use spinlocks and might be called
> : before lockdep is initialized.  Particularly this line in the
> : reserve_ebda_region function causes problem:
> : 
> : lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
> : 
> : If i put lockdep_init() before reserve_ebda_region call in
> : x86_64_start_reservations kernel loads well.
> 
> Fix this ordering issue permanently: change lockdep so that it uses hlists
> for the hash tables.  Unlike a list_head, an hlist_head is in its
> initialized state when it is all-zeroes, so lockdep is ready for operation
> immediately upon boot - lockdep_init() need not have run.
> 
> The patch will also save some memory.
> 
> lockdep_init() and lockdep_initialized can be done away with now - a 4.6
> patch has been prepared to do this.
> 
> Reported-by: Mike Krinkin <krinkin.m.u@xxxxxxxxx>
> Suggested-by: Mike Krinkin <krinkin.m.u@xxxxxxxxx>
> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> 
>  include/linux/lockdep.h  |    4 +--
>  kernel/locking/lockdep.c |   42 ++++++++++++++++---------------------
>  2 files changed, 21 insertions(+), 25 deletions(-)

Hm, so I already have the patch below queued up for v4.6, in the locking tree, 
plus the followup lockdep_init() patch as well.

Didn't want to merge this relatively intrusive patch late in the -rc cycle, as it 
appears this is not a regression: CONFIG_UBSAN_ALIGNMENT apparently never worked 
on x86_64.

But no big feelings either way.

Thanks,

	Ingo

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