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Subject[PATCH 1/1] mm: msync: fix issues of sys_msync on tmpfs
Date
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@windriver.com>
---
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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