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mm/msync.c: sync only the requested range in msync()

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msync() currently syncs more than POSIX requires or BSD or Solaris
implement.  It is supposed to be equivalent to fdatasync(), not fsync(),
and it is only supposed to sync the portion of the file that overlaps the
range passed to msync.

If the VMA is non-linear, fall back to syncing the entire file, but we
still optimise to only fdatasync() the entire file, not the full fsync().

akpm: there are obvious concerns with bck-compatibility: is anyone relying
on the undocumented side-effect for their data integrity?  And how would
they ever know if this change broke their data integrity?

We think the risk is reasonably low, and this patch brings the kernel into
line with other OS's and with what the manpage has always said...

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Chris Mason <clm@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Wilcox 2014-06-04 16:10:44 -07:00 committed by Linus Torvalds
parent 65eb71823b
commit 7fc34a62ca
1 changed files with 7 additions and 1 deletions
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8
mm/msync.c
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@ -58,6 +58,7 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
vma = find_vma(mm, start);
for (;;) {
struct file *file;
loff_t fstart, fend;
/* Still start < end. */
error = -ENOMEM;
@ -77,12 +78,17 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
goto out_unlock;
}
file = vma->vm_file;
fstart = start + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
fend = fstart + (min(end, vma->vm_end) - start) - 1;
start = vma->vm_end;
if ((flags & MS_SYNC) && file &&
(vma->vm_flags & VM_SHARED)) {
get_file(file);
up_read(&mm->mmap_sem);
error = vfs_fsync(file, 0);
if (vma->vm_flags & VM_NONLINEAR)
error = vfs_fsync(file, 1);
else
error = vfs_fsync_range(file, fstart, fend, 1);
fput(file);
if (error || start >= end)
goto out;