NTFS: Fix a mount time deadlock.

Big thanks go to Mathias Kolehmainen for reporting the bug, providing
debug output and testing the patches I sent him to get it working.

The fix was to stop calling ntfs_attr_set() at mount time as that causes
balance_dirty_pages_ratelimited() to be called which on systems with
little memory actually tries to go and balance the dirty pages which tries
to take the s_umount semaphore but because we are still in fill_super()
across which the VFS holds s_umount for writing this results in a
deadlock.

We now do the dirty work by hand by submitting individual buffers.  This
has the annoying "feature" that mounting can take a few seconds if the
journal is large as we have clear it all.  One day someone should improve
on this by deferring the journal clearing to a helper kernel thread so it
can be done in the background but I don't have time for this at the moment
and the current solution works fine so I am leaving it like this for now.

Signed-off-by: Anton Altaparmakov <aia21@cantab.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
index 1c08fefe487a..92dabdcf2b80 100644
--- a/fs/ntfs/attrib.c
+++ b/fs/ntfs/attrib.c
@@ -1,7 +1,7 @@
 /**
  * attrib.c - NTFS attribute operations.  Part of the Linux-NTFS project.
  *
- * Copyright (c) 2001-2006 Anton Altaparmakov
+ * Copyright (c) 2001-2007 Anton Altaparmakov
  * Copyright (c) 2002 Richard Russon
  *
  * This program/include file is free software; you can redistribute it and/or
@@ -2500,7 +2500,7 @@ int ntfs_attr_set(ntfs_inode *ni, const s64 ofs, const s64 cnt, const u8 val)
         struct page *page;
         u8 *kaddr;
         pgoff_t idx, end;
-        unsigned int start_ofs, end_ofs, size;
+        unsigned start_ofs, end_ofs, size;
 
         ntfs_debug("Entering for ofs 0x%llx, cnt 0x%llx, val 0x%hx.",
                         (long long)ofs, (long long)cnt, val);
@@ -2548,6 +2548,8 @@ int ntfs_attr_set(ntfs_inode *ni, const s64 ofs, const s64 cnt, const u8 val)
                 kunmap_atomic(kaddr, KM_USER0);
                 set_page_dirty(page);
                 page_cache_release(page);
+                balance_dirty_pages_ratelimited(mapping);
+                cond_resched();
                 if (idx == end)
                         goto done;
                 idx++;
@@ -2604,6 +2606,8 @@ int ntfs_attr_set(ntfs_inode *ni, const s64 ofs, const s64 cnt, const u8 val)
                 kunmap_atomic(kaddr, KM_USER0);
                 set_page_dirty(page);
                 page_cache_release(page);
+                balance_dirty_pages_ratelimited(mapping);
+                cond_resched();
         }
 done:
         ntfs_debug("Done.");