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authorXin Zhong <xin.zhong@intel.com>2010-12-09 09:30:14 +0000
committerChris Mason <chris.mason@oracle.com>2010-12-10 16:29:10 -0500
commit914ee295af418e936ec20a08c1663eaabe4cd07a (patch)
tree2e880ea913b8cbadf22b2288b5c278c2e5eadb60 /fs
parentf106e82caaa0d943e47cacc184f5b40d538e0044 (diff)
Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
This problem is found in meego testing: http://bugs.meego.com/show_bug.cgi?id=6672 A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to write to the same page of the same file. In btrfs_file_aio_write(), the pages is locked by prepare_pages(). So when btrfs_copy_from_user() is called, page fault happens and the same page needs to be locked again in filemap_fault(). The fix is to move iov_iter_fault_in_readable() before prepage_pages() to make page fault happen before pages are locked. And also disable page fault in critical region in btrfs_copy_from_user(). Reviewed-by: Yan, Zheng<zheng.z.yan@intel.com> Signed-off-by: Zhong, Xin <xin.zhong@intel.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/btrfs/file.c92
1 files changed, 60 insertions, 32 deletions
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index c1faded5fca..66836d85763 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -48,30 +48,34 @@ static noinline int btrfs_copy_from_user(loff_t pos, int num_pages,
struct page **prepared_pages,
struct iov_iter *i)
{
- size_t copied;
+ size_t copied = 0;
int pg = 0;
int offset = pos & (PAGE_CACHE_SIZE - 1);
+ int total_copied = 0;
while (write_bytes > 0) {
size_t count = min_t(size_t,
PAGE_CACHE_SIZE - offset, write_bytes);
struct page *page = prepared_pages[pg];
-again:
- if (unlikely(iov_iter_fault_in_readable(i, count)))
- return -EFAULT;
-
- /* Copy data from userspace to the current page */
- copied = iov_iter_copy_from_user(page, i, offset, count);
+ /*
+ * Copy data from userspace to the current page
+ *
+ * Disable pagefault to avoid recursive lock since
+ * the pages are already locked
+ */
+ pagefault_disable();
+ copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
+ pagefault_enable();
/* Flush processor's dcache for this page */
flush_dcache_page(page);
iov_iter_advance(i, copied);
write_bytes -= copied;
+ total_copied += copied;
+ /* Return to btrfs_file_aio_write to fault page */
if (unlikely(copied == 0)) {
- count = min_t(size_t, PAGE_CACHE_SIZE - offset,
- iov_iter_single_seg_count(i));
- goto again;
+ break;
}
if (unlikely(copied < PAGE_CACHE_SIZE - offset)) {
@@ -81,7 +85,7 @@ again:
offset = 0;
}
}
- return 0;
+ return total_copied;
}
/*
@@ -854,6 +858,8 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
unsigned long last_index;
int will_write;
int buffered = 0;
+ int copied = 0;
+ int dirty_pages = 0;
will_write = ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
(file->f_flags & O_DIRECT));
@@ -970,7 +976,17 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
WARN_ON(num_pages > nrptrs);
memset(pages, 0, sizeof(struct page *) * nrptrs);
- ret = btrfs_delalloc_reserve_space(inode, write_bytes);
+ /*
+ * Fault pages before locking them in prepare_pages
+ * to avoid recursive lock
+ */
+ if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ ret = btrfs_delalloc_reserve_space(inode,
+ num_pages << PAGE_CACHE_SHIFT);
if (ret)
goto out;
@@ -978,37 +994,49 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
pos, first_index, last_index,
write_bytes);
if (ret) {
- btrfs_delalloc_release_space(inode, write_bytes);
+ btrfs_delalloc_release_space(inode,
+ num_pages << PAGE_CACHE_SHIFT);
goto out;
}
- ret = btrfs_copy_from_user(pos, num_pages,
+ copied = btrfs_copy_from_user(pos, num_pages,
write_bytes, pages, &i);
- if (ret == 0) {
+ dirty_pages = (copied + PAGE_CACHE_SIZE - 1) >>
+ PAGE_CACHE_SHIFT;
+
+ if (num_pages > dirty_pages) {
+ if (copied > 0)
+ atomic_inc(
+ &BTRFS_I(inode)->outstanding_extents);
+ btrfs_delalloc_release_space(inode,
+ (num_pages - dirty_pages) <<
+ PAGE_CACHE_SHIFT);
+ }
+
+ if (copied > 0) {
dirty_and_release_pages(NULL, root, file, pages,
- num_pages, pos, write_bytes);
+ dirty_pages, pos, copied);
}
btrfs_drop_pages(pages, num_pages);
- if (ret) {
- btrfs_delalloc_release_space(inode, write_bytes);
- goto out;
- }
- if (will_write) {
- filemap_fdatawrite_range(inode->i_mapping, pos,
- pos + write_bytes - 1);
- } else {
- balance_dirty_pages_ratelimited_nr(inode->i_mapping,
- num_pages);
- if (num_pages <
- (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
- btrfs_btree_balance_dirty(root, 1);
- btrfs_throttle(root);
+ if (copied > 0) {
+ if (will_write) {
+ filemap_fdatawrite_range(inode->i_mapping, pos,
+ pos + copied - 1);
+ } else {
+ balance_dirty_pages_ratelimited_nr(
+ inode->i_mapping,
+ dirty_pages);
+ if (dirty_pages <
+ (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
+ btrfs_btree_balance_dirty(root, 1);
+ btrfs_throttle(root);
+ }
}
- pos += write_bytes;
- num_written += write_bytes;
+ pos += copied;
+ num_written += copied;
cond_resched();
}