Re: FAILED: patch "[PATCH] pipe: increase minimum default pipe size to 2 pages" failed to apply to 4.4-stable tree

["Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>]

Excerpts from Greg Kroah-Hartman's message of August 9, 2021 12:27 pm:
> On Mon, Aug 09, 2021 at 09:23:00AM -0700, Linus Torvalds wrote:
>> On Mon, Aug 9, 2021 at 2:52 AM <gregkh@linuxfoundation.org> wrote:
>> >
>> > The patch below does not apply to the 4.4-stable tree.
>> 
>> It shouldn't.
>> 
>> The pipe buffer accounting and soft limits that introduced the whole
>> "limp along with limited pipe buffers" behavior that this fixes was
>> introduced by
>> 
>> > Fixes: 759c01142a ("pipe: limit the per-user amount of pages allocated in pipes")
>> 
>> ..which made it into 4.5.
>> 
>> So 4.4 is unaffected and doesn't want this patch.
> 
> But that commit showed up in 4.4.13 as fa6d0ba12a8e ("pipe: limit the
> per-user amount of pages allocated in pipes") which is why I asked about
> this.  The code didn't look similar at all, so I couldn't easily figure
> out the backport myself :(
> 
> Willy, any ideas?
> 
> thanks,
> 
> greg k-h
> 

alloc_pipe_info was heavily modified in 09b4d19900 ("pipe: simplify 
logic in alloc_pipe_info()") and a005ca0e68 ("pipe: fix limit checking 
in alloc_pipe_info()"), which I think landed in 4.9 and weren't 
backported. The backported patch should look similar to this:

@@ -621,7 +621,7 @@

                if (!too_many_pipe_buffers_hard(user)) {
                        if (too_many_pipe_buffers_soft(user))
-                               pipe_bufs = 1;
+                               pipe_bufs = 2;
                        pipe->bufs = kzalloc(sizeof(struct pipe_buffer) * pipe_bufs, GFP_KERNEL);
                }

I can send a rebased patch, but I think we can also leave it the way it 
is. It's a bit of an edge case; if nobody's hit it so far on 4.4, maybe 
it can just stay this way until February. There's SLTS, but I don't 
think they're interested in this kind of patch. Thoughts?

Cheers,
Alex.