Commit 201913ed authored by Ryusuke Konishi's avatar Ryusuke Konishi
Browse files

nilfs2: fix circular locking dependency of writer mutex



This fixes the following circular locking dependency problem:

 =======================================================
 [ INFO: possible circular locking dependency detected ]
 2.6.30-rc3 #5
 -------------------------------------------------------
 segctord/3895 is trying to acquire lock:
  (&nilfs->ns_writer_mutex){+.+...}, at: [<d0d02172>]
   nilfs_mdt_get_block+0x89/0x20f [nilfs2]

 but task is already holding lock:
  (&bmap->b_sem){++++..}, at: [<d0d02d99>]
   nilfs_bmap_propagate+0x14/0x2e [nilfs2]

 which lock already depends on the new lock.

The bugfix is done by replacing call sites of nilfs_get_writer() which
are never called from read-only context with direct dereferencing of
pointer to a writable FS-instance.
Signed-off-by: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
parent 85c2a74f
......@@ -516,14 +516,16 @@ static ssize_t
nilfs_ioctl_do_free_segments(struct the_nilfs *nilfs, __u64 *posp, int flags,
void *buf, size_t size, size_t nmembs)
{
struct nilfs_sb_info *sbi = nilfs_get_writer(nilfs);
struct nilfs_sb_info *sbi = nilfs->ns_writer;
int ret;
if (unlikely(!sbi))
if (unlikely(!sbi)) {
/* never happens because called for a writable mount */
WARN_ON(1);
return -EROFS;
}
ret = nilfs_segctor_add_segments_to_be_freed(
NILFS_SC(sbi), buf, nmembs);
nilfs_put_writer(nilfs);
return (ret < 0) ? ret : nmembs;
}
......
......@@ -77,19 +77,22 @@ static int nilfs_mdt_create_block(struct inode *inode, unsigned long block,
void *))
{
struct the_nilfs *nilfs = NILFS_MDT(inode)->mi_nilfs;
struct nilfs_sb_info *writer = NULL;
struct super_block *sb = inode->i_sb;
struct nilfs_transaction_info ti;
struct buffer_head *bh;
int err;
if (!sb) {
writer = nilfs_get_writer(nilfs);
if (!writer) {
/*
* Make sure this function is not called from any
* read-only context.
*/
if (!nilfs->ns_writer) {
WARN_ON(1);
err = -EROFS;
goto out;
}
sb = writer->s_super;
sb = nilfs->ns_writer->s_super;
}
nilfs_transaction_begin(sb, &ti, 0);
......@@ -127,8 +130,6 @@ static int nilfs_mdt_create_block(struct inode *inode, unsigned long block,
err = nilfs_transaction_commit(sb);
else
nilfs_transaction_abort(sb);
if (writer)
nilfs_put_writer(nilfs);
out:
return err;
}
......
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