Re: [PATCH 1/2] mm: fix missing handler for __GFP_NOWARN

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On 2022/5/10 7:38 PM, Qi Zheng wrote:
We expect no warnings to be issued when we specify __GFP_NOWARN, but
currently in paths like alloc_pages() and kmalloc(), there are still
some warnings printed, fix it.

Hi Andrew,

Maybe we only need to deal with memory allocation failures, such as
should_fail() (This leads to deadlock in PATCH[2/2]). These WARN_ON_ONCE()s report usage problems and should not be printed. If they
are printed, we should fix these usage problems.

Thanks,
Qi



Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
  include/linux/fault-inject.h |  2 ++
  lib/fault-inject.c           |  3 +++
  mm/failslab.c                |  3 +++
  mm/internal.h                | 11 +++++++++++
  mm/page_alloc.c              | 22 ++++++++++++----------
  5 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h
index 2d04f6448cde..9f6e25467844 100644
--- a/include/linux/fault-inject.h
+++ b/include/linux/fault-inject.h
@@ -20,6 +20,7 @@ struct fault_attr {
  	atomic_t space;
  	unsigned long verbose;
  	bool task_filter;
+	bool no_warn;
  	unsigned long stacktrace_depth;
  	unsigned long require_start;
  	unsigned long require_end;
@@ -39,6 +40,7 @@ struct fault_attr {
  		.ratelimit_state = RATELIMIT_STATE_INIT_DISABLED,	\
  		.verbose = 2,						\
  		.dname = NULL,						\
+		.no_warn = false,					\
  	}
#define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER
diff --git a/lib/fault-inject.c b/lib/fault-inject.c
index ce12621b4275..423784d9c058 100644
--- a/lib/fault-inject.c
+++ b/lib/fault-inject.c
@@ -41,6 +41,9 @@ EXPORT_SYMBOL_GPL(setup_fault_attr);
static void fail_dump(struct fault_attr *attr)
  {
+	if (attr->no_warn)
+		return;
+
  	if (attr->verbose > 0 && __ratelimit(&attr->ratelimit_state)) {
  		printk(KERN_NOTICE "FAULT_INJECTION: forcing a failure.\n"
  		       "name %pd, interval %lu, probability %lu, "
diff --git a/mm/failslab.c b/mm/failslab.c
index f92fed91ac23..58df9789f1d2 100644
--- a/mm/failslab.c
+++ b/mm/failslab.c
@@ -30,6 +30,9 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
  	if (failslab.cache_filter && !(s->flags & SLAB_FAILSLAB))
  		return false;
+ if (gfpflags & __GFP_NOWARN)
+		failslab.attr.no_warn = true;
+
  	return should_fail(&failslab.attr, s->object_size);
  }
diff --git a/mm/internal.h b/mm/internal.h
index cf16280ce132..7a268fac6559 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -35,6 +35,17 @@ struct folio_batch;
  /* Do not use these with a slab allocator */
  #define GFP_SLAB_BUG_MASK (__GFP_DMA32|__GFP_HIGHMEM|~__GFP_BITS_MASK)
+#define WARN_ON_ONCE_GFP(cond, gfp) ({ \
+	static bool __section(".data.once") __warned;			\
+	int __ret_warn_once = !!(cond);					\
+									\
+	if (unlikely(!(gfp & __GFP_NOWARN) && __ret_warn_once && !__warned)) { \
+		__warned = true;					\
+		WARN_ON(1);						\
+	}								\
+	unlikely(__ret_warn_once);					\
+})
+
  void page_writeback_init(void);
static inline void *folio_raw_mapping(struct folio *folio)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0e42038382c1..2bf4ce4d0e2f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3722,7 +3722,7 @@ struct page *rmqueue(struct zone *preferred_zone,
  	 * We most definitely don't want callers attempting to
  	 * allocate greater than order-1 page units with __GFP_NOFAIL.
  	 */
-	WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
+	WARN_ON_ONCE_GFP((gfp_flags & __GFP_NOFAIL) && (order > 1), gfp_flags);
do {
  		page = NULL;
@@ -3799,6 +3799,9 @@ static bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
  			(gfp_mask & __GFP_DIRECT_RECLAIM))
  		return false;
+ if (gfp_mask & __GFP_NOWARN)
+		fail_page_alloc.attr.no_warn = true;
+
  	return should_fail(&fail_page_alloc.attr, 1 << order);
  }
@@ -4346,7 +4349,8 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
  	 */
/* Exhausted what can be done so it's blame time */
-	if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) {
+	if (out_of_memory(&oc) ||
+	    WARN_ON_ONCE_GFP(gfp_mask & __GFP_NOFAIL, gfp_mask)) {
  		*did_some_progress = 1;
/*
@@ -4902,8 +4906,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
  	 * We also sanity check to catch abuse of atomic reserves being used by
  	 * callers that are not in atomic context.
  	 */
-	if (WARN_ON_ONCE((gfp_mask & (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)) ==
-				(__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)))
+	if (WARN_ON_ONCE_GFP((gfp_mask & (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)) ==
+				(__GFP_ATOMIC|__GFP_DIRECT_RECLAIM), gfp_mask))
  		gfp_mask &= ~__GFP_ATOMIC;
retry_cpuset:
@@ -5117,7 +5121,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
  		 * All existing users of the __GFP_NOFAIL are blockable, so warn
  		 * of any new users that actually require GFP_NOWAIT
  		 */
-		if (WARN_ON_ONCE(!can_direct_reclaim))
+		if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask))
  			goto fail;
/*
@@ -5125,7 +5129,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
  		 * because we cannot reclaim anything and only can loop waiting
  		 * for somebody to do a work for us
  		 */
-		WARN_ON_ONCE(current->flags & PF_MEMALLOC);
+		WARN_ON_ONCE_GFP(current->flags & PF_MEMALLOC, gfp_mask);
/*
  		 * non failing costly orders are a hard requirement which we
@@ -5133,7 +5137,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
  		 * so that we can identify them and convert them to something
  		 * else.
  		 */
-		WARN_ON_ONCE(order > PAGE_ALLOC_COSTLY_ORDER);
+		WARN_ON_ONCE_GFP(order > PAGE_ALLOC_COSTLY_ORDER, gfp_mask);
/*
  		 * Help non-failing allocations by giving them access to memory
@@ -5379,10 +5383,8 @@ struct page *__alloc_pages(gfp_t gfp, unsigned int order, int preferred_nid,
  	 * There are several places where we assume that the order value is sane
  	 * so bail out early if the request is out of bound.
  	 */
-	if (unlikely(order >= MAX_ORDER)) {
-		WARN_ON_ONCE(!(gfp & __GFP_NOWARN));
+	if (WARN_ON_ONCE_GFP(order >= MAX_ORDER, gfp))
  		return NULL;
-	}
gfp &= gfp_allowed_mask;
  	/*

--
Thanks,
Qi




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