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    SubjectRe: swap_cluster_info lockdep splat
    Date
    Hi, Hugh,

    Hugh Dickins <hughd@google.com> writes:

    > On Thu, 16 Feb 2017, Tim Chen wrote:
    >>
    >> > I do not understand your zest for putting wrappers around every little
    >> > thing, making it all harder to follow than it need be.  Here's the patch
    >> > I've been running with (but you have a leak somewhere, and I don't have
    >> > time to search out and fix it: please try sustained swapping and swapoff).
    >> >
    >>
    >> Hugh, trying to duplicate your test case.  So you were doing swapping,
    >> then swap off, swap on the swap device and restart swapping?
    >
    > Repeated pair of make -j20 kernel builds in 700M RAM, 1.5G swap on SSD,
    > 8 cpus; one of the builds in tmpfs, other in ext4 on loop on tmpfs file;
    > sizes tuned for plenty of swapping but no OOMing (it's an ancient 2.6.24
    > kernel I build, modern one needing a lot more space with a lot less in use).
    >
    > How much of that is relevant I don't know: hopefully none of it, it's
    > hard to get the tunings right from scratch. To answer your specific
    > question: yes, I'm not doing concurrent swapoffs in this test showing
    > the leak, just waiting for each of the pair of builds to complete,
    > then tearing down the trees, doing swapoff followed by swapon, and
    > starting a new pair of builds.
    >
    > Sometimes it's the swapoff that fails with ENOMEM, more often it's a
    > fork during build that fails with ENOMEM: after 6 or 7 hours of load
    > (but timings show it getting slower leading up to that). /proc/meminfo
    > did not give me an immediate clue, Slab didn't look surprising but
    > I may not have studied close enough.
    >
    > I quilt-bisected it as far as the mm-swap series, good before, bad
    > after, but didn't manage to narrow it down further because of hitting
    > a presumably different issue inside the series, where swapoff ENOMEMed
    > much sooner (after 25 mins one time, during first iteration the next).

    I found a memory leak in __read_swap_cache_async() introduced by mm-swap
    series, and confirmed it via testing. Could you verify whether it fixed
    your cases? Thanks a lot for reporting.

    Best Regards,
    Huang, Ying

    ------------------------------------------------------------------------->
    From 4b96423796ab7435104eb2cb4dcf5d525b9e0800 Mon Sep 17 00:00:00 2001
    From: Huang Ying <ying.huang@intel.com>
    Date: Fri, 17 Feb 2017 10:31:37 +0800
    Subject: [PATCH] mm, swap: Fix memory leak in __read_swap_cache_async()

    The memory may be leaked in __read_swap_cache_async(). For the cases
    as below,

    CPU 0 CPU 1
    ----- -----

    find_get_page() == NULL
    __swp_swapcount() != 0
    new_page = alloc_page_vma()
    radix_tree_maybe_preload()
    swap in swap slot
    swapcache_prepare() == -EEXIST
    cond_resched()
    reclaim the swap slot
    find_get_page() == NULL
    __swp_swapcount() == 0
    return NULL <- new_page leaked here !!!

    The memory leak has been confirmed via checking the value of new_page
    when returning inside the loop in __read_swap_cache_async().

    This is fixed via replacing return with break inside of loop in
    __read_swap_cache_async(), so that there is opportunity for the
    new_page to be checked and freed.

    Reported-by: Hugh Dickins <hughd@google.com>
    Cc: Tim Chen <tim.c.chen@linux.intel.com>
    Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
    ---
    mm/swap_state.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/mm/swap_state.c b/mm/swap_state.c
    index 2126e9ba23b2..473b71e052a8 100644
    --- a/mm/swap_state.c
    +++ b/mm/swap_state.c
    @@ -333,7 +333,7 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
    * else swap_off will be aborted if we return NULL.
    */
    if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
    - return NULL;
    + break;

    /*
    * Get a new page to read into from swap.
    --
    2.11.0
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