From: Mike Galbraith <umgwanakikbuti@xxxxxxxxx> Subject: zsmalloc: replace get_cpu_var with local_lock The usage of get_cpu_var() in zs_map_object() is problematic because it disables preemption and makes it impossible to acquire any sleeping lock on PREEMPT_RT such as a spinlock_t. Replace the get_cpu_var() usage with a local_lock_t which is embedded struct mapping_area. It ensures that the access the struct is synchronized against all users on the same CPU. [minchan: remove the bit_spin_lock part and change the title] Link: https://lkml.kernel.org/r/20211115185909.3949505-10-minchan@xxxxxxxxxx Signed-off-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> Tested-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Cc: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/zsmalloc.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) --- a/mm/zsmalloc.c~zsmalloc-replace-get_cpu_var-with-local_lock +++ a/mm/zsmalloc.c @@ -65,6 +65,7 @@ #include <linux/wait.h> #include <linux/pagemap.h> #include <linux/fs.h> +#include <linux/local_lock.h> #define ZSPAGE_MAGIC 0x58 @@ -276,6 +277,7 @@ struct zspage { }; struct mapping_area { + local_lock_t lock; char *vm_buf; /* copy buffer for objects that span pages */ char *vm_addr; /* address of kmap_atomic()'ed pages */ enum zs_mapmode vm_mm; /* mapping mode */ @@ -451,7 +453,9 @@ MODULE_ALIAS("zpool-zsmalloc"); #endif /* CONFIG_ZPOOL */ /* per-cpu VM mapping areas for zspage accesses that cross page boundaries */ -static DEFINE_PER_CPU(struct mapping_area, zs_map_area); +static DEFINE_PER_CPU(struct mapping_area, zs_map_area) = { + .lock = INIT_LOCAL_LOCK(lock), +}; static __maybe_unused int is_first_page(struct page *page) { @@ -1269,7 +1273,8 @@ void *zs_map_object(struct zs_pool *pool class = zspage_class(pool, zspage); off = (class->size * obj_idx) & ~PAGE_MASK; - area = &get_cpu_var(zs_map_area); + local_lock(&zs_map_area.lock); + area = this_cpu_ptr(&zs_map_area); area->vm_mm = mm; if (off + class->size <= PAGE_SIZE) { /* this object is contained entirely within a page */ @@ -1320,7 +1325,7 @@ void zs_unmap_object(struct zs_pool *poo __zs_unmap_object(area, pages, off, class->size); } - put_cpu_var(zs_map_area); + local_unlock(&zs_map_area.lock); migrate_read_unlock(zspage); } _
