[yocto] [V2 PATCH 1/1] mm: msync: fix issues of sys_msync on tmpfs

[Zumeng Chen]

There are two problems as follows shown:
1 ) for TMPFS, nothing need to be done in sys_msync,
    sys_msync just return 0 for all arches.

2 ) But for MIPS CPUs with cache alias(dmesg|grep alias),
    it maybe has the issue, which reported by msync test
    suites in ltp-full, when the memory of memset used by
    msycn01 has cache alias.
    So, in this situation, we have to flush the related
    vma to make sure correct read.

Signed-off-by: Zumeng Chen <zumeng.chen at windriver.com>
---
 include/linux/shmem_fs.h |   10 ++++++++++
 mm/msync.c               |   22 +++++++++++++++++++++-
 mm/shmem.c               |    5 +++++
 3 files changed, 36 insertions(+), 1 deletions(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index aa08fa8..62a2d57 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -12,6 +12,15 @@
 
 #define SHMEM_SYMLINK_INLINE_LEN (SHMEM_NR_DIRECT * sizeof(swp_entry_t))
 
+/*
+
+*/
+#ifndef cpu_has_dc_aliases
+#define CPU_HAS_CACHE_ALIAS 0
+#else
+#define CPU_HAS_CACHE_ALIAS cpu_has_dc_aliases
+#endif
+
 struct shmem_inode_info {
 	spinlock_t		lock;
 	unsigned long		flags;
@@ -49,6 +58,7 @@ static inline struct shmem_inode_info *SHMEM_I(struct inode *inode)
 /*
  * Functions in mm/shmem.c called directly from elsewhere:
  */
+extern int is_shmem_file(struct file *file);
 extern int init_tmpfs(void);
 extern int shmem_fill_super(struct super_block *sb, void *data, int silent);
 extern struct file *shmem_file_setup(const char *name,
diff --git a/mm/msync.c b/mm/msync.c
index 632df45..84cb068 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -13,6 +13,8 @@
 #include <linux/file.h>
 #include <linux/syscalls.h>
 #include <linux/sched.h>
+#include <linux/shmem_fs.h>
+#include <asm/cacheflush.h>
 
 /*
  * MS_SYNC syncs the entire file - including mappings.
@@ -33,6 +35,7 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
 	unsigned long end;
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
+	struct file *file;
 	int unmapped_error = 0;
 	int error = -EINVAL;
 
@@ -56,8 +59,25 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
 	 */
 	down_read(&mm->mmap_sem);
 	vma = find_vma(mm, start);
+
+#ifdef CONFIG_TMPFS
+	/*
+	 * For tmpfs, no matter which flag(ASYNC or SYNC) gets from msync,
+	 * there is not so much thing to do for CPUs without cache alias,
+	 * But for some CPUs with cache alias, msync has to flush cache
+	 * explicitly, which makes sure the data coherency between memory
+	 * file and cache.
+	 */
+	file =  vma->vm_file;
+	if (is_shmem_file(file)) {
+		if(CPU_HAS_CACHE_ALIAS)
+			flush_cache_range(vma, start, start+len);
+		error = 0;
+		goto out_unlock;
+	}
+#endif
+
 	for (;;) {
-		struct file *file;
 
 		/* Still start < end. */
 		error = -ENOMEM;
diff --git a/mm/shmem.c b/mm/shmem.c
index 92e5c15..4fabfac 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2793,6 +2793,11 @@ static struct file_system_type tmpfs_fs_type = {
 	.kill_sb	= kill_litter_super,
 };
 
+int is_shmem_file(struct file *file)
+{
+	return (file->f_op == &shmem_file_operations)? 1 : 0;
+} 
+
 int __init init_tmpfs(void)
 {
 	int error;
-- 
1.7.5.4