Re: [PATCH] mm/page_alloc: Correct return value of populated elements if bulk array is populated

[Geert Uytterhoeven]

Hi Mel,

On Mon, Jun 28, 2021 at 5:29 PM Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote:
> Dave Jones reported the following
>
>         This made it into 5.13 final, and completely breaks NFSD for me
>         (Serving tcp v3 mounts).  Existing mounts on clients hang, as do
>         new mounts from new clients.  Rebooting the server back to rc7
>         everything recovers.
>
> The commit b3b64ebd3822 ("mm/page_alloc: do bulk array bounds check after
> checking populated elements") returns the wrong value if the array is
> already populated which is interpreted as an allocation failure. Dave
> reported this fixes his problem and it also passed a test running dbench
> over NFS.
>
> Fixes: b3b64ebd3822 ("mm/page_alloc: do bulk array bounds check after checking populated elements")
> Reported-and-tested-by: Dave Jones <davej@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> [5.13+]

I saw similar failures as Mike Galbraith when doing s2idle or s2ram
on some boards with some configs:

    Freezing of tasks failed after 20.004 seconds (1 tasks refusing to
freeze, wq_busy=0):
    task:NFSv4 callback  state:S stack:    0 pid:  280 ppid:     2
flags:0x00000000
    [<c094b634>] (__schedule) from [<c094b8d0>] (schedule+0xc0/0x110)
    [<c094b8d0>] (schedule) from [<c094faec>] (schedule_timeout+0xc8/0x108)
    [<c094faec>] (schedule_timeout) from [<c092e0a0>] (svc_recv+0x108/0xa30)
    [<c092e0a0>] (svc_recv) from [<c04c5990>] (nfs4_callback_svc+0x6c/0x84)
    [<c04c5990>] (nfs4_callback_svc) from [<c0244ddc>] (kthread+0x128/0x138)
    [<c0244ddc>] (kthread) from [<c0200114>] (ret_from_fork+0x14/0x20)

I've bisected it (twice, as I couldn't believe the result) to the
same commit, which helped me find the fix.

After cherry-picking commit 66d9282523b32281 ("mm/page_alloc: Correct
return value of populated elements if bulk array is populated"),
the problem went away.

Tested-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds