[PATCH v1 2/2] mm/show_mem: Add trylock while printing alloc info

[Yueyang Pan]

In production, show_mem() can be called concurrently from two
different entities, for example one from oom_kill_process()
another from __alloc_pages_slowpath from another kthread. This
patch adds a mutex and invokes trylock before printing out the
kernel alloc info in show_mem(). This way two alloc info won't
interleave with each other, which then makes parsing easier.

Signed-off-by: Yueyang Pan <pyyjason@xxxxxxxxx>
---
 mm/show_mem.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/show_mem.c b/mm/show_mem.c
index b71e222fde86..8814b5f8a7dc 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -23,6 +23,8 @@ EXPORT_SYMBOL(_totalram_pages);
 unsigned long totalreserve_pages __read_mostly;
 unsigned long totalcma_pages __read_mostly;
 
+static DEFINE_MUTEX(mem_alloc_profiling_mutex);
+
 static inline void show_node(struct zone *zone)
 {
 	if (IS_ENABLED(CONFIG_NUMA))
@@ -419,7 +421,7 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
 	printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages));
 #endif
 #ifdef CONFIG_MEM_ALLOC_PROFILING
-	if (mem_alloc_profiling_enabled()) {
+	if (mem_alloc_profiling_enabled() && mutex_trylock(&mem_alloc_profiling_mutex)) {
 		struct codetag_bytes tags[10];
 		size_t i, nr;
 
@@ -445,6 +447,7 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
 						  ct->lineno, ct->function);
 			}
 		}
+		mutex_unlock(&mem_alloc_profiling_mutex);
 	}
 #endif
 }
-- 
2.47.3