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

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Message-ID: <2c4bdc7a-b49f-c2ea-28d0-4ec838c3b26c@oracle.com>
Date:   Sat, 2 Jul 2022 01:18:09 +1000
From:   Imran Khan <imran.f.khan@...cle.com>
To:     Nathan Chancellor <nathan@...nel.org>
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.

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.

Could you please suggest me if I should send a v2 of this change with these tags
included or if this mail is enough. Sorry if I am asking something obvious but I
am encountering such situation for first time.

Thanks
-- Imran