Re: [PATCH 2/3] mm: Extract might_alloc() debug check

[Jason Gunthorpe <jgg@xxxxxxxx>]

On Fri, Nov 20, 2020 at 10:54:43AM +0100, Daniel Vetter wrote:
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index d5ece7a9a403..f94405d43fd1 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -180,6 +180,22 @@ 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));
> +}

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Oh, I just had a another thread with Matt about xarray, this would be
perfect to add before xas_nomem():

diff --git a/lib/idr.c b/lib/idr.c
index f4ab4f4aa3c7f5..722d9ddff53221 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -391,6 +391,8 @@ int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max,
 	if ((int)max < 0)
 		max = INT_MAX;
 
+	might_alloc(gfp);
+
 retry:
 	xas_lock_irqsave(&xas, flags);
 next:
diff --git a/lib/xarray.c b/lib/xarray.c
index 5fa51614802ada..dd260ee7dcae9a 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1534,6 +1534,8 @@ void *__xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
 	XA_STATE(xas, xa, index);
 	void *curr;
 
+	might_alloc(gfp);
+
 	if (WARN_ON_ONCE(xa_is_advanced(entry)))
 		return XA_ERROR(-EINVAL);
 	if (xa_track_free(xa) && !entry)
@@ -1600,6 +1602,8 @@ void *__xa_cmpxchg(struct xarray *xa, unsigned long index,
 	XA_STATE(xas, xa, index);
 	void *curr;
 
+	might_alloc(gfp);
+
 	if (WARN_ON_ONCE(xa_is_advanced(entry)))
 		return XA_ERROR(-EINVAL);
 
@@ -1637,6 +1641,8 @@ int __xa_insert(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
 	XA_STATE(xas, xa, index);
 	void *curr;
 
+	might_alloc(gfp);
+
 	if (WARN_ON_ONCE(xa_is_advanced(entry)))
 		return -EINVAL;
 	if (!entry)
@@ -1806,6 +1812,8 @@ int __xa_alloc(struct xarray *xa, u32 *id, void *entry,
 {
 	XA_STATE(xas, xa, 0);
 
+	might_alloc(gfp);
+
 	if (WARN_ON_ONCE(xa_is_advanced(entry)))
 		return -EINVAL;
 	if (WARN_ON_ONCE(!xa_track_free(xa)))