Re: [PATCH] fsfreeze: tell hung_task about processes put to sleep

[Fernando Luis Vazquez Cao <fernando_b1@lab.ntt.co.jp>]

On 2012年10月15日 15:36, Dave Chinner wrote:
> On Mon, Oct 15, 2012 at 12:24:59PM +0900, Fernando Luis Vazquez Cao wrote:
>> On 2012/10/13 10:06, Dave Chinner wrote:
>>> On Fri, Oct 12, 2012 at 06:47:32PM +0900, Fernando Luis Vázquez Cao wrote:
>>>> Any process attempting to write to a frozen filesystem uninterruptibly and
>>>> unkillably waits for the filesystem to be thawed. This wait is of unbounded
>>>> length. Ignore such waits in the hung_task detector.
>>> Filesystems should not be frozen for long enough to trigger the hung
>>> task detector under normal usage. IMO, if you are freezing a
>>> filesystem for that long, then you're either doing something wrong
>>> or something has gone wrong, and in either case I think we should be
>>> emitting warnings...
>> The problem is that in production systems situations where
>> a filesystem remains brozen for long periods are not uncommon.
>> A typical example is as follows: the control daemon or script that
>> controls the freeze/thaw using the fsfreeze ioctls dies, the next
> There's your problem. Fix that, don't turn off useful warnings that
> indicate something has gone wrong.

It is not my problem. It is the enterprise distro's user's problem.

As I mentioned in my previous email if you want to emit a
warning do it in the right place and make sure that it is
something informative. hung_check certainly isn't the
right place to do it.

A failure in a user space script should not lead to a kernel
panic or to a flood of process stack dumps in the system log
administrators cannot interpret (a common complaint from
our customers). This is the behaviour this patch is trying to
fix.

Thanks,
Fernando
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