linux-kernel - Re: [PATCH] kernfs: Avoid re-adding kernfs_node into kernfs_notify

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Message-ID: <Yr8T8nJC+HyPj8F7@dev-arch.thelio-3990X>
Date:   Fri, 1 Jul 2022 08:34:10 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Imran Khan <imran.f.khan@...cle.com>
Cc:     tj@...nel.org, gregkh@...uxfoundation.org, viro@...iv.linux.org.uk,
        m.szyprowski@...sung.com, michael@...le.cc, robh@...nel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        guillaume.tucker@...labora.com, pmladek@...e.com
Subject: Re: [PATCH] kernfs: Avoid re-adding kernfs_node into
 kernfs_notify_list.

On Sat, Jul 02, 2022 at 01:18:09AM +1000, Imran Khan wrote:
> Hello Nathan,
> 
> On 2/7/22 1:10 am, Nathan Chancellor wrote:
> > On Sat, Jul 02, 2022 at 12:50:47AM +1000, Imran Khan wrote:
> >> Kick fsnotify only if an event is not already scheduled for target
> >> kernfs node. commit b8f35fa1188b ("kernfs: Change kernfs_notify_list to
> >> llist.") changed kernfs_notify_list to a llist.
> >> Prior to this list was a singly linked list, protected by
> >> kernfs_notify_lock. Whenever a kernfs_node was added to the list
> >> its ->attr.notify_next was set to head of the list and upon removal
> >> ->attr.notify_next was reset to NULL. Addition to kernfs_notify_list
> >> would only happen if kernfs_node was not already in the list i.e.
> >> if ->attr.notify_next was NULL. commit b8f35fa1188b ("kernfs: Change
> >> kernfs_notify_list to llist.") removed this checking and this was wrong
> >> as it resulted in multiple additions for same kernfs_node.
> >>
> >> So far this bug only got reflected with some console related setting.
> >> Nathan found this issue when console was specified both in DT and in
> >> kernel command line and Marek found this issue when earlycon was enabled.
> >>
> >> This patch avoids adding an already added kernfs_node into notify list.
> >>
> >> Reported-by: Nathan Chancellor <nathan@...nel.org>
> >> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> > 
> > This should also include:
> > 
> > Reported-by: Michael Walle <michael@...le.cc>
> > 
> >> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
> >> Fixes: b8f35fa1188b ("kernfs: Change kernfs_notify_list to llist.")
> >> Signed-off-by: Imran Khan <imran.f.khan@...cle.com>
> > 
> > For the ARCH=um case that I noticed:
> > 
> > Tested-by: Nathan Chancellor <nathan@...nel.org>
> > 
> 
> I am really sorry about missing these tags. I was not sure if you have tested
> the patch I sent this morning.

No worries, we all forget tags :) I hadn't tested your patch until this
point so there was no reason for you to add that tag, this was the first
time I provided it so there is no problem there. Thanks for the quick
fix!

Cheers,
Nathan