git: 942951ba46ec - main - uma dbg: catch more corruption with atomics

[Michal Meloun]

On 31.12.2020 22:03, Ryan Libby wrote:
> The branch main has been updated by rlibby:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=942951ba46ecd5ebab18de006a24dc52e2d3f745
> 
> commit 942951ba46ecd5ebab18de006a24dc52e2d3f745
> Author:     Ryan Libby <rlibby at FreeBSD.org>
> AuthorDate: 2020-12-31 21:02:45 +0000
> Commit:     Ryan Libby <rlibby at FreeBSD.org>
> CommitDate: 2020-12-31 21:02:45 +0000
> 
>      uma dbg: catch more corruption with atomics
>      
>      Use atomic testandset and testandclear to catch concurrent double free,
>      and to reduce the number of atomic operations.
>      
>      Submitted by:   jeff
>      Reviewed by:    cem, kib, markj (all previous version)
>      Sponsored by:   Dell EMC Isilon
>      Differential Revision:  https://reviews.freebsd.org/D22703
Unfortunately, this broke arm and arm64 kernel with random
'duplicate alloc'/'duplicate free' panics.

Michal

> ---
>   sys/vm/uma_core.c | 9 ++++-----
>   1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
> index a0192642205d..39c846effac8 100644
> --- a/sys/vm/uma_core.c
> +++ b/sys/vm/uma_core.c
> @@ -5392,10 +5392,10 @@ uma_dbg_alloc(uma_zone_t zone, uma_slab_t slab, void *item)
>   	keg = zone->uz_keg;
>   	freei = slab_item_index(slab, keg, item);
>   
> -	if (BIT_ISSET(keg->uk_ipers, freei, slab_dbg_bits(slab, keg)))
> +	if (BIT_TEST_SET_ATOMIC(keg->uk_ipers, freei,
> +	    slab_dbg_bits(slab, keg)))
>   		panic("Duplicate alloc of %p from zone %p(%s) slab %p(%d)",
>   		    item, zone, zone->uz_name, slab, freei);
> -	BIT_SET_ATOMIC(keg->uk_ipers, freei, slab_dbg_bits(slab, keg));
>   }
>   
>   /*
> @@ -5426,11 +5426,10 @@ uma_dbg_free(uma_zone_t zone, uma_slab_t slab, void *item)
>   		panic("Unaligned free of %p from zone %p(%s) slab %p(%d)",
>   		    item, zone, zone->uz_name, slab, freei);
>   
> -	if (!BIT_ISSET(keg->uk_ipers, freei, slab_dbg_bits(slab, keg)))
> +	if (!BIT_TEST_CLR_ATOMIC(keg->uk_ipers, freei,
> +	    slab_dbg_bits(slab, keg)))
>   		panic("Duplicate free of %p from zone %p(%s) slab %p(%d)",
>   		    item, zone, zone->uz_name, slab, freei);
> -
> -	BIT_CLR_ATOMIC(keg->uk_ipers, freei, slab_dbg_bits(slab, keg));
>   }
>   #endif /* INVARIANTS */
>   
>