On Mon, Jan 09, 2012 at 06:05:32PM +0100, Miklos Szeredi wrote:
> Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes:
>
> > On Mon, Jan 9, 2012 at 2:58 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> >>
> >> This patch adds a new dentry flag that is set when the dentry is removed
> >> from the lru and put on the list being processed by
> >> shrink_dentry_list(). The flag is cleared in dentry_lru_del() which is
> >> called if the dentry gets a new reference just before it's pruned.
> >>
> >> Thoughts?
> >
> > Looks reasonable. Were you actually able to reproduce the hang, or how
> > did you notice?
>
> We got a bug report from a partner about hang during reboot. It's
> actually quite easily reproducible with:
>
> while true; do
> echo -bond0 > /sys/class/net/bonding_masters
> echo +bond0 > /sys/class/net/bonding_masters
> echo -bond1 > /sys/class/net/bonding_masters
> echo +bond1 > /sys/class/net/bonding_masters
> done
>
> That reliably triggers the soft lookup detector for several machines
> that we tested. It's rather timing sensitive though, because turning on
> DEBUG_SPINLOCK makes it go away.
>
> I had to add printks to see what's going on, because it wasn't obvious
> from the stack traces and crash dumps.
You also usually need to add a udev rule that looks at the pci id of the
device as well, without checking for what type it is (which is what a
"correct" udev rule should be doing, which is why we only started seeing
this on some systems, with "incorrect" rules.)
Having a file in /lib/udev/rules.d/ with only this one rule:
ATTR{vendor}=="0x8086", ATTR{device}=="0x10ca", ENV{PCI_SLOT_NAME}="%k", ENV{MATCHADDR}="$attr{address}", RUN+="/bin/true"
Seems to do the trick. udev calls stat() on the vendor sysfs file,
while it is going away, and then this dentry race shows up.
thanks,
greg k-h
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