linux-kernel - Re: [PATCH v2] genalloc: Make the avail variable an atomic_long

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Date:   Thu, 26 Oct 2017 16:22:19 +0000 (UTC)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Stephen Bates <sbates@...thlin.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Daniel Mentz <danielmentz@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will.deacon@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        logang <logang@...tatee.com>
Subject: Re: [PATCH v2] genalloc: Make the avail variable an atomic_long_t

----- On Oct 26, 2017, at 6:04 PM, Stephen Bates sbates@...thlin.com wrote:

> From: Stephen Bates <sbates@...thlin.com>
> 
> If the amount of resources allocated to a gen_pool exceeds 2^32 then
> the avail atomic overflows and this causes problems when clients try
> and borrow resources from the pool. This is only expected to be an
> issue on 64 bit systems.
> 
> Add the <linux/atomic.h> header to pull in atomic_long* operations. So
> that 32 bit systems continue to use atomic32_t but 64 bit systems can
> use atomic64_t.
> 
> Changes since v1:
>  Change atomic64 to atomic_long as per Mathieu
>  Added a Reviewed-by tag from Logan
> 
> Signed-off-by: Stephen Bates <sbates@...thlin.com>
> Reviewed-by: Logan Gunthorpe <logang@...tatee.com>

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

> ---
> include/linux/genalloc.h |  3 ++-
> lib/genalloc.c           | 10 +++++-----
> 2 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/genalloc.h b/include/linux/genalloc.h
> index 6dfec4d..872f930 100644
> --- a/include/linux/genalloc.h
> +++ b/include/linux/genalloc.h
> @@ -32,6 +32,7 @@
> 
> #include <linux/types.h>
> #include <linux/spinlock_types.h>
> +#include <linux/atomic.h>
> 
> struct device;
> struct device_node;
> @@ -71,7 +72,7 @@ struct gen_pool {
>  */
> struct gen_pool_chunk {
> 	struct list_head next_chunk;	/* next chunk in pool */
> -	atomic_t avail;
> +	atomic_long_t avail;
> 	phys_addr_t phys_addr;		/* physical starting address of memory chunk */
> 	unsigned long start_addr;	/* start address of memory chunk */
> 	unsigned long end_addr;		/* end address of memory chunk (inclusive) */
> diff --git a/lib/genalloc.c b/lib/genalloc.c
> index 144fe6b..ca06adc 100644
> --- a/lib/genalloc.c
> +++ b/lib/genalloc.c
> @@ -194,7 +194,7 @@ int gen_pool_add_virt(struct gen_pool *pool, unsigned long
> virt, phys_addr_t phy
> 	chunk->phys_addr = phys;
> 	chunk->start_addr = virt;
> 	chunk->end_addr = virt + size - 1;
> -	atomic_set(&chunk->avail, size);
> +	atomic_long_set(&chunk->avail, size);
> 
> 	spin_lock(&pool->lock);
> 	list_add_rcu(&chunk->next_chunk, &pool->chunks);
> @@ -304,7 +304,7 @@ unsigned long gen_pool_alloc_algo(struct gen_pool *pool,
> size_t size,
> 	nbits = (size + (1UL << order) - 1) >> order;
> 	rcu_read_lock();
> 	list_for_each_entry_rcu(chunk, &pool->chunks, next_chunk) {
> -		if (size > atomic_read(&chunk->avail))
> +		if (size > atomic_long_read(&chunk->avail))
> 			continue;
> 
> 		start_bit = 0;
> @@ -324,7 +324,7 @@ unsigned long gen_pool_alloc_algo(struct gen_pool *pool,
> size_t size,
> 
> 		addr = chunk->start_addr + ((unsigned long)start_bit << order);
> 		size = nbits << order;
> -		atomic_sub(size, &chunk->avail);
> +		atomic_long_sub(size, &chunk->avail);
> 		break;
> 	}
> 	rcu_read_unlock();
> @@ -390,7 +390,7 @@ void gen_pool_free(struct gen_pool *pool, unsigned long
> addr, size_t size)
> 			remain = bitmap_clear_ll(chunk->bits, start_bit, nbits);
> 			BUG_ON(remain);
> 			size = nbits << order;
> -			atomic_add(size, &chunk->avail);
> +			atomic_long_add(size, &chunk->avail);
> 			rcu_read_unlock();
> 			return;
> 		}
> @@ -464,7 +464,7 @@ size_t gen_pool_avail(struct gen_pool *pool)
> 
> 	rcu_read_lock();
> 	list_for_each_entry_rcu(chunk, &pool->chunks, next_chunk)
> -		avail += atomic_read(&chunk->avail);
> +		avail += atomic_long_read(&chunk->avail);
> 	rcu_read_unlock();
> 	return avail;
> }
> --
> 2.7.4

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com