Re: [PATCH] Fix sysrq emergency thaw

Re: [PATCH] Fix sysrq emergency thaw

[Chris Mason]

On 07/15/2016 08:38 PM, Charles Gong wrote:
> "SYSRQ + J" triggers a call to emergency_thaw_all(). Currently, this is an
> infinite loop. Once we trigger it, we'll need to do a hard power-cycle. There
> are users reporting this bug from 2012 to 2016, for example, at
> https://bugzilla.kernel.org/show_bug.cgi?id=47741.
>
> This happens because thaw_bdev() fails to return -EINVAL in the non-frozen case,
> and I fixed it so that do_one_thaw() can recognize this case and quit from
> looping. I checked that none of the other thaw_bdev() callers check the return
> value.

Hi Charles,

Can you please resend this without the hunks that change only 
whitespace?  Looks like your editor was properly killing off trailing 
whitespace, but that's not related to your fix.

Also, please reference the commit where the regression was introduced:

commit 4504230a71566785a05d3e6b53fa1ee071b864eb
Author: Christoph Hellwig <hch@lst.de>
Date:   Mon Aug 3 23:28:35 2009 +0200

     freeze_bdev: grab active reference to frozen superblocks

Then you can add:

Reviewed-by: Chris Mason <clm@fb.com>

Thanks!

-chris

Re: [PATCH] Fix sysrq emergency thaw

[Pavel Machek]

On Wed 2016-07-20 16:11:16, Charles Gong wrote:
> "SYSRQ + J" triggers a call to emergency_thaw_all(). Currently, this
> is an infinite loop. Once we trigger it, we'll need to do a hard
> power-cycle. There are users reporting this bug from 2012 to 2016, for
> example, at https://bugzilla.kernel.org/show_bug.cgi?id=47741.
> 
> This happens because thaw_bdev() fails to return -EINVAL in the
> non-frozen case, so fix it so that do_one_thaw() can recognize this case
> and quit from looping. I checked that none of the other thaw_bdev()
> callers check the return value.
> 
> The regression was introduced in commit 4504230a7156 ("freeze_bdev: grab
> active reference to frozen superblocks").
> 
> Reviewed-by: Chris Mason <clm@fb.com>
> Signed-off-by: Charles Gong <cggong@fb.com>

Acked-by: Pavel Machek <pavel@ucw.cz>

(even magic should be finite...)
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html