[yocto] [V3 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 but MIPS.

2 ) 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
    msync01 runs into cache alias randomly.

    Consider the following scenario used by msync01 in ltp-full:
	fildes = open(TEMPFILE, O_RDWR | O_CREAT, 0666)) < 0);
	.../* initialization fildes by write(fildes); */
	addr = mmap(0, page_sz, PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED,
		fildes, 0);
	/* set buf with memset */
        memset(addr + OFFSET_1, 1, BUF_SIZE);

        /* msync the addr before using */
	msync(addr, page_sz, MS_ASYNC)

	/* Then tries to read fildes */
	lseek(fildes, (off_t) OFFSET_1, SEEK_SET) != (off_t) OFFSET_1) {
	nread = read(fildes, read_buf, sizeof(read_buf));

	/* Then tries to test the result */
	if (read_buf[count] != 1) {

    The test result is random too for CPUs with cache alias. So
    in this situation, we have to flush the related vma to make
    sure the read is correct.

Signed-off-by: Zumeng Chen <zumeng.chen at windriver.com>
---
 include/linux/shmem_fs.h |   10 ++++++++++
 mm/msync.c               |   22 +++++++++++++++++++++-
 mm/shmem.c               |    4 ++--
 3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index aa08fa8..349f8fe 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))
 
+/*
+ * MIPS cache alias should be taken into accounts when msync.
+ */
+#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 const struct file_operations shmem_file_operations;
 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..ced6215 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 (file && (file->f_op == &shmem_file_operations)) {
+		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 fcedf54..f848fd3 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -222,7 +222,7 @@ static inline void shmem_unacct_blocks(unsigned long flags, long pages)
 
 static const struct super_operations shmem_ops;
 static const struct address_space_operations shmem_aops;
-static const struct file_operations shmem_file_operations;
+const struct file_operations shmem_file_operations;
 static const struct inode_operations shmem_inode_operations;
 static const struct inode_operations shmem_dir_inode_operations;
 static const struct inode_operations shmem_special_inode_operations;
@@ -2692,7 +2692,7 @@ static const struct address_space_operations shmem_aops = {
 	.error_remove_page = generic_error_remove_page,
 };
 
-static const struct file_operations shmem_file_operations = {
+const struct file_operations shmem_file_operations = {
 	.mmap		= shmem_mmap,
 #ifdef CONFIG_TMPFS
 	.llseek		= generic_file_llseek,
-- 
1.7.5.4