Commit a3726599 authored by Mike Galbraith's avatar Mike Galbraith Committed by Linus Torvalds
Browse files

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@kernel.org


Signed-off-by: default avatarMike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarMinchan Kim <minchan@kernel.org>
Tested-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b475d42d

mm/zsmalloc.c

+8 −3
Original line number Diff line number Diff line
@@ -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, unsigned long handle, 
	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 *pool, unsigned long handle) 


		__zs_unmap_object(area, pages, off, class->size);

	}

	put_cpu_var(zs_map_area);

	local_unlock(&zs_map_area.lock);



	migrate_read_unlock(zspage);

}