On Wed, 1 May 2013 09:56:13 -0400 Robert Love <rlove@xxxxxxxxxx> wrote:
> Don't acquire ashmem_mutex in ashmem_shrink if we've somehow recursed into the
> shrinker code from within ashmem. Just bail out, avoiding a deadlock. This is
> fine, as ashmem cache pruning is advisory anyhow.
>
Sorry, but I don't think "somehow" is an adequate description of a
kernel bug. The deadlock should be described with specificity, so that
others can understand and review the fix and perhaps suggest
alternative implementations.
Presumably someone is performing a memory allocation while holding
ashmem_mutex. A more idiomatic way of avoiding a call to direct
reclaim in these circumstances would be for the task to set its
PF_MEMALLOC flag, or to use GFP_ATOMIC. But without any details that's
as far as I can go.
> --- a/drivers/staging/android/ashmem.c
> +++ b/drivers/staging/android/ashmem.c
> @@ -363,7 +363,11 @@ static int ashmem_shrink(struct shrinker *s, struct shrink_control *sc)
> if (!sc->nr_to_scan)
> return lru_count;
>
> - mutex_lock(&ashmem_mutex);
> + /* avoid recursing into this code from within ashmem itself */
> + if (!mutex_trylock(&ashmem_mutex)) {
> + return -1;
> + }
This is rather hacky. It consumes more CPU than the above approaches,
and more stack.
Worst of all, it obviously hasn't met checkpatch.pl ;)
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