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

[Zumeng Chen]

This patch fixes two issues as follows:

For some filesystem with fsync == noop_fsync, there is not so much thing
to do, so sys_msync just passes by for all arches but some CPUs.

For some CPUs with cache aliases(dmesg|grep alias), it maybe has an 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, or MS_SYNC*/
  msync(addr, page_sz, MS_ASYNC)

  /* 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 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@xxxxxxxxxxxxx>
---
 mm/msync.c |   30 ++++++++++++++++++++++++++++++
 1 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/mm/msync.c b/mm/msync.c
index 632df45..0021a7e 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -13,6 +13,14 @@
 #include <linux/file.h>
 #include <linux/syscalls.h>
 #include <linux/sched.h>
+#include <asm/cacheflush.h>
+
+/* Cache aliases should be taken into accounts when msync. */
+#ifdef cpu_has_dc_aliases
+#define CPU_HAS_CACHE_ALIAS cpu_has_dc_aliases
+#else
+#define CPU_HAS_CACHE_ALIAS 0
+#endif
 
 /*
  * MS_SYNC syncs the entire file - including mappings.
@@ -78,6 +86,28 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
 		}
 		file = vma->vm_file;
 		start = vma->vm_end;
+
+		/*
+		 * For some filesystems with fsync == noop_fsync, msync just
+		 * passes by but some CPUs.
+		 * For CPUs with cache alias, msync has to flush the related
+		 * vma explicitly to make sure data coherency between memory
+		 * and cache, which includes MS_SYNC or MS_ASYNC. That is to
+		 * say, cache aliases should not be an async factor, so does
+		 * msync on other arches without cache aliases.
+		 */
+		if (file && file->f_op && file->f_op->fsync == noop_fsync) {
+			if (CPU_HAS_CACHE_ALIAS)
+				flush_cache_range(vma, vma->vm_start,
+							vma->vm_end);
+			if (start >= end) {
+				error = 0;
+				goto out_unlock;
+			}
+			vma = find_vma(mm, start);
+			continue;
+		}
+
 		if ((flags & MS_SYNC) && file &&
 				(vma->vm_flags & VM_SHARED)) {
 			get_file(file);
-- 
1.7.0.4

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