[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>

diff --git a/mm/msync.c b/mm/msync.c
index 8a66f5d5d4f0d5cda1a14bb265ddef30ca6e9ac0..ee9bd67598330439b759ea5d158de8060f307a16 100644 (file)
--- 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;
                }