Re: fs/dcache.c - BUG: soft lockup - CPU#5 stuck for 22s! [systemd-udevd:1667]

[Al Viro <viro@ZenIV.linux.org.uk>]

On Wed, May 28, 2014 at 10:37:51AM +0300, Mika Westerberg wrote:

> I sent you the whole log privately so that I don't spam everyone.
> 
> Summary is here:
> 
> May 28 10:24:23 lahna kernel: scsi 14:0:0:0: Direct-Access     JetFlash Transcend 4GB    8.07 PQ: 0 ANSI: 4
> May 28 10:24:23 lahna kernel: sd 14:0:0:0: Attached scsi generic sg4 type 0
> May 28 10:24:23 lahna kernel: sd 14:0:0:0: [sdc] 7864320 512-byte logical blocks: (4.02 GB/3.75 GiB)
> May 28 10:24:23 lahna kernel: sd 14:0:0:0: [sdc] Write Protect is off
> May 28 10:24:23 lahna kernel: sd 14:0:0:0: [sdc] Mode Sense: 23 00 00 00
> May 28 10:24:23 lahna kernel: sd 14:0:0:0: [sdc] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
> May 28 10:24:23 lahna kernel:  sdc: sdc1
> May 28 10:24:23 lahna kernel: sd 14:0:0:0: [sdc] Attached SCSI removable disk
> 
> Here I detached the USB stick:
> 
> May 28 10:24:32 lahna kernel: usb 3-10.4: USB disconnect, device number 6
> May 28 10:24:32 lahna kernel: check_submounts_and_drop[/dev/block/8:33]; CPU 4 PID 576 [systemd-udevd]
> May 28 10:24:32 lahna kernel: dput[/dev/block/8:33]; CPU 4 PID 576 [systemd-udevd]
> May 28 10:24:32 lahna kernel: check_submounts_and_drop[3-10/3-10.4/3-10.4:1.0/host14]; CPU 1 PID 1683 [systemd-udevd]
> May 28 10:24:32 lahna kernel: shrink[3-10.4:1.0/host14/target14:0:0/subsystem]; CPU 1 PID 1683 [systemd-udevd]
> May 28 10:24:32 lahna kernel: shrink[host14/target14:0:0/14:0:0:0/rev]; CPU 1 PID 1683 [systemd-udevd]
> May 28 10:24:32 lahna kernel: shrink[host14/target14:0:0/14:0:0:0/vendor]; CPU 1 PID 1683 [systemd-udevd]
> May 28 10:24:32 lahna kernel: shrink[host14/target14:0:0/14:0:0:0/model]; CPU 1 PID 1683 [systemd-udevd]
> May 28 10:24:32 lahna kernel: check_submounts_and_drop[/dev/block/8:32]; CPU 4 PID 576 [systemd-udevd]
> ...
> May 28 10:24:32 lahna kernel: check_submounts_and_drop[0000:00:14.0/usb3/3-10/3-10.4]; CPU 6 PID 1684 [systemd-udevd]
> May 28 10:24:32 lahna kernel: check_submounts_and_drop[0000:00:14.0/usb3/3-10/3-10.4]; CPU 7 PID 1685 [systemd-udevd]
> May 28 10:24:32 lahna kernel: shrink[usb3/3-10/3-10.4/ltm_capable]; CPU 7 PID 1685 [systemd-udevd]
> May 28 10:24:32 lahna kernel: A
...

Hmm...  As it is, we have d_walk() trying _very_ hard in those situations.
Could you add that on top of the previous and see if livelock changes?

diff --git a/fs/dcache.c b/fs/dcache.c
index 42ae01e..4ce58d3 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1209,7 +1209,7 @@ static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
 	 * ensures forward progress). We'll be coming back to find
 	 * the rest.
 	 */
-	if (!list_empty(&data->dispose))
+	if (data->found)
 		ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
 out:
 	return ret;