Commit 22c963ad authored Apr 14, 2009 by Frederic Weisbecker

kill-the-BKL/reiserfs: lock only once in reiserfs_truncate_file



Impact: fix a deadlock

reiserfs_truncate_file() can be called from multiple context where
the write lock can be already hold or not.

This function also acquire (possibly recursively) the write
lock. Subsequent releases before sleeping will not actually release
the lock because we may be in more than one lock depth degree.

A typical case is:

reiserfs_file_release {
	acquire_the_lock()
	reiserfs_truncate_file()
		reacquire_the_lock()
		journal_begin() {
			do_journal_begin_r() {
				reiserfs_wait_on_write_block() {
					/*
					 * Not released because still one
					 * depth owned
					 */
					release_lock()
					wait_for_event()

At this stage the event never happen because the one which provides
it needs the write lock.

We use reiserfs_write_lock_once() here to ensure that we don't acquire the
write lock recursively.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@texware.it>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Alexander Beregalov <a.beregalov@gmail.com>
Cc: Chris Mason <chris.mason@oracle.com>
LKML-Reference: <1239680065-25013-3-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent daf88c89

fs/reiserfs/inode.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -2079,8 +2079,9 @@ int reiserfs_truncate_file(struct inode *inode, int update_timestamps)
		int error;
		struct buffer_head *bh = NULL;
		int err2;
		int lock_depth;

		reiserfs_write_lock(inode->i_sb);
		lock_depth = reiserfs_write_lock_once(inode->i_sb);

		if (inode->i_size > 0) {
		error = grab_tail_page(inode, &page, &bh);
		@@ -2149,14 +2150,17 @@ int reiserfs_truncate_file(struct inode *inode, int update_timestamps)
		page_cache_release(page);
		}

		reiserfs_write_unlock(inode->i_sb);
		reiserfs_write_unlock_once(inode->i_sb, lock_depth);

		return 0;
		out:
		if (page) {
		unlock_page(page);
		page_cache_release(page);
		}
		reiserfs_write_unlock(inode->i_sb);

		reiserfs_write_unlock_once(inode->i_sb, lock_depth);

		return error;
		}

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