On Sun, Jan 08, 2012 at 03:04:30PM -0800, Linus Torvalds wrote: > Hmm. > > Al, Miklos, I just triggered the new inc_link() warning three times in > very close succession by just doing a simple > > perf record -f -e cycles:pp make -j > > (I don't think the "perf record" part was actually required or > relevant, although it may have been instrumental in triggering just > the right timing) > > This was in a fully built tree, I'm just checking > > The warning trace looks like this: > > [ 6933.446125] ------------[ cut here ]------------ > [ 6933.446131] WARNING: at fs/inode.c:349 inc_nlink+0x30/0x40() > [ 6933.446133] Hardware name: System Product Name > [ 6933.446135] Pid: 22955, comm: perf Not tainted > 3.2.0-03190-g972b2c719990 #72 > [ 6933.446137] Call Trace: > [ 6933.446143] [<ffffffff8102ee15>] warn_slowpath_common+0x75/0xb0 > [ 6933.446145] [<ffffffff8102ef15>] warn_slowpath_null+0x15/0x20 > [ 6933.446147] [<ffffffff810f1450>] inc_nlink+0x30/0x40 > [ 6933.446151] [<ffffffff8116f333>] ext4_symlink+0x113/0x2c0 > [ 6933.446154] [<ffffffff810e7b01>] vfs_symlink+0xa1/0xf0 > [ 6933.446157] [<ffffffff810e7c03>] sys_symlinkat+0xb3/0xd0 > [ 6933.446159] [<ffffffff810e7c31>] sys_symlink+0x11/0x20 > [ 6933.446162] [<ffffffff816916a2>] system_call_fastpath+0x16/0x1b > [ 6933.446164] ---[ end trace 550d4b2eb6b8fbc9 ]--- > > and the three warnings all triggered within 2/100th of a second of > that one (the last one had a timestamp of 6933.465678), so they are > probably all related to the same thing happening. WTF is ext4_symlink() doing in case of long symlinks? Look: drop_nlink(inode); err = ext4_orphan_add(handle, inode); ext4_journal_stop(handle); [write symlink body] inc_nlink(inode); err = ext4_orphan_del(handle, inode); oh, I see... The comment above that re deadlocks and inability to do that in a single transaction ;-/ OK, try this; that's equivalent to what they are doing and will not WARN_ON(); I hadn't checked other filesystems for similar tricks yet, so this has a good chance of being incomplete. diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index 86edc45..2043f48 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -2315,7 +2315,7 @@ retry: err = PTR_ERR(handle); goto err_drop_inode; } - inc_nlink(inode); + set_nlink(inode, 1); err = ext4_orphan_del(handle, inode); if (err) { ext4_journal_stop(handle); -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html