[PATCH] msync(MS_SYNC): don't hold mmap_sem while syncing

It seems bad to hold mmap_sem while performing synchronous disk I/O.  Alter
the msync(MS_SYNC) code so that the lock is released while we sync the file.

Cc: Hugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 26 insertions, 23 deletions

diff --git a/mm/msync.c b/mm/msync.c
index 8a66f5d5d4f0..ee9bd6759833 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -132,35 +132,14 @@ static int msync_interval(struct vm_area_struct *vma, unsigned long addr,
                         unsigned long end, int flags,
                         unsigned long *nr_pages_dirtied)
 {
-        int ret = 0;
         struct file *file = vma->vm_file;
 
         if ((flags & MS_INVALIDATE) && (vma->vm_flags & VM_LOCKED))
                 return -EBUSY;
 
-        if (file && (vma->vm_flags & VM_SHARED)) {
+        if (file && (vma->vm_flags & VM_SHARED))
                 *nr_pages_dirtied = msync_page_range(vma, addr, end);
-
-                if (flags & MS_SYNC) {
-                        struct address_space *mapping = file->f_mapping;
-                        int err;
-
-                        ret = filemap_fdatawrite(mapping);
-                        if (file->f_op && file->f_op->fsync) {
-                                /*
-                                 * We don't take i_mutex here because mmap_sem
-                                 * is already held.
-                                 */
-                                err = file->f_op->fsync(file,file->f_dentry,1);
-                                if (err && !ret)
-                                        ret = err;
-                        }
-                        err = filemap_fdatawait(mapping);
-                        if (!ret)
-                                ret = err;
-                }
-        }
-        return ret;
+        return 0;
 }
 
 asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
@@ -233,6 +212,30 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
                         fput(file);
                         down_read(&current->mm->mmap_sem);
                         vma = find_vma(current->mm, start);
+                } else if ((flags & MS_SYNC) && file &&
+                                (vma->vm_flags & VM_SHARED)) {
+                        struct address_space *mapping;
+                        int err;
+
+                        get_file(file);
+                        up_read(&current->mm->mmap_sem);
+                        mapping = file->f_mapping;
+                        error = filemap_fdatawrite(mapping);
+                        if (file->f_op && file->f_op->fsync) {
+                                mutex_lock(&mapping->host->i_mutex);
+                                err = file->f_op->fsync(file,file->f_dentry,1);
+                                mutex_unlock(&mapping->host->i_mutex);
+                                if (err && !error)
+                                        error = err;
+                        }
+                        err = filemap_fdatawait(mapping);
+                        if (err && !error)
+                                error = err;
+                        fput(file);
+                        down_read(&current->mm->mmap_sem);
+                        if (error)
+                                goto out_unlock;
+                        vma = find_vma(current->mm, start);
                 } else {
                         vma = vma->vm_next;
                 }