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nilfs2: fix circular locking dependency of writer mutex

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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: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
This commit is contained in:
Ryusuke Konishi
2009-04-28 21:04:59 +09:00
parent 85c2a74fab
commit 201913ed74
2 changed files with 12 additions and 9 deletions
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8
fs/nilfs2/ioctl.c
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@@ -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;
}