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Date:   Sat, 2 Jul 2022 01:18:09 +1000
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Subject: Re: [PATCH] kernfs: Avoid re-adding kernfs_node into
 kernfs_notify_list.
Content-Language: en-US
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     tj@kernel.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk,
        m.szyprowski@samsung.com, michael@walle.cc, robh@kernel.org,
        linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
        guillaume.tucker@collabora.com, pmladek@suse.com
References: <20220701145047.2206900-1-imran.f.khan@oracle.com>
 <Yr8OSxotW2VEUyKQ@dev-arch.thelio-3990X>
From:   Imran Khan <imran.f.khan@oracle.com>
In-Reply-To: <Yr8OSxotW2VEUyKQ@dev-arch.thelio-3990X>
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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@kernel.org>
>> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> 
> This should also include:
> 
> Reported-by: Michael Walle <michael@walle.cc>
> 
>> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
>> Fixes: b8f35fa1188b ("kernfs: Change kernfs_notify_list to llist.")
>> Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
> 
> For the ARCH=um case that I noticed:
> 
> Tested-by: Nathan Chancellor <nathan@kernel.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