On Fri, Oct 23, 2020 at 02:21:15PM +0200, Daniel Vetter wrote:
> Extracted from slab.h, which seems to have the most complete version
> including the correct might_sleep() check. Roll it out to slob.c.
>
> Motivated by a discussion with Paul about possibly changing call_rcu
> behaviour to allocate memory, but only roughly every 500th call.
>
> There are a lot fewer places in the kernel that care about whether
> allocating memory is allowed or not (due to deadlocks with reclaim
> code) than places that care whether sleeping is allowed. But debugging
> these also tends to be a lot harder, so nice descriptive checks could
> come in handy. I might have some use eventually for annotations in
> drivers/gpu.
>
> Note that unlike fs_reclaim_acquire/release gfpflags_allow_blocking
> does not consult the PF_MEMALLOC flags. But there is no flag
> equivalent for GFP_NOWAIT, hence this check can't go wrong due to
> memalloc_no*_save/restore contexts.
>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Cc: Michel Lespinasse <walken@xxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Waiman Long <longman@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
> Cc: Qian Cai <cai@xxxxxx>
> Cc: linux-xfs@xxxxxxxxxxxxxxx
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Nice!!!
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
> include/linux/sched/mm.h | 16 ++++++++++++++++
> mm/slab.h | 5 +----
> mm/slob.c | 6 ++----
> 3 files changed, 19 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index f889e332912f..2b0037abac0b 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -205,6 +205,22 @@ static inline void fs_reclaim_acquire(gfp_t gfp_mask) { }
> static inline void fs_reclaim_release(gfp_t gfp_mask) { }
> #endif
>
> +/**
> + * might_alloc - Marks possible allocation sites
> + * @gfp_mask: gfp_t flags that would be use to allocate
> + *
> + * Similar to might_sleep() and other annotations this can be used in functions
> + * that might allocate, but often dont. Compiles to nothing without
> + * CONFIG_LOCKDEP. Includes a conditional might_sleep() if @gfp allows blocking.
> + */
> +static inline void might_alloc(gfp_t gfp_mask)
> +{
> + fs_reclaim_acquire(gfp_mask);
> + fs_reclaim_release(gfp_mask);
> +
> + might_sleep_if(gfpflags_allow_blocking(gfp_mask));
> +}
> +
> /**
> * memalloc_noio_save - Marks implicit GFP_NOIO allocation scope.
> *
> diff --git a/mm/slab.h b/mm/slab.h
> index 6cc323f1313a..fedd789b2270 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -492,10 +492,7 @@ static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
> {
> flags &= gfp_allowed_mask;
>
> - fs_reclaim_acquire(flags);
> - fs_reclaim_release(flags);
> -
> - might_sleep_if(gfpflags_allow_blocking(flags));
> + might_alloc(flags);
>
> if (should_failslab(s, flags))
> return NULL;
> diff --git a/mm/slob.c b/mm/slob.c
> index 7cc9805c8091..8d4bfa46247f 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -474,8 +474,7 @@ __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
>
> gfp &= gfp_allowed_mask;
>
> - fs_reclaim_acquire(gfp);
> - fs_reclaim_release(gfp);
> + might_alloc(gfp);
>
> if (size < PAGE_SIZE - minalign) {
> int align = minalign;
> @@ -597,8 +596,7 @@ static void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
>
> flags &= gfp_allowed_mask;
>
> - fs_reclaim_acquire(flags);
> - fs_reclaim_release(flags);
> + might_alloc(flags);
>
> if (c->size < PAGE_SIZE) {
> b = slob_alloc(c->size, flags, c->align, node, 0);
> --
> 2.28.0
>
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