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    Subject[PATCH AUTOSEL 5.1 133/141] proc: use down_read_killable mmap_sem for /proc/pid/smaps_rollup
    Date
    From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

    [ Upstream commit a26a97815548574213fd37f29b4b78ccc6d9ed20 ]

    Do not remain stuck forever if something goes wrong. Using a killable
    lock permits cleanup of stuck tasks and simplifies investigation.

    Link: http://lkml.kernel.org/r/156007493429.3335.14666825072272692455.stgit@buzz
    Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
    Reviewed-by: Roman Gushchin <guro@fb.com>
    Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
    Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
    Acked-by: Michal Hocko <mhocko@suse.com>
    Cc: Alexey Dobriyan <adobriyan@gmail.com>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Michal Koutný <mkoutny@suse.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/proc/task_mmu.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
    index 95ca1fe7283c..c5b1b6db9a70 100644
    --- a/fs/proc/task_mmu.c
    +++ b/fs/proc/task_mmu.c
    @@ -828,7 +828,10 @@ static int show_smaps_rollup(struct seq_file *m, void *v)

    memset(&mss, 0, sizeof(mss));

    - down_read(&mm->mmap_sem);
    + ret = down_read_killable(&mm->mmap_sem);
    + if (ret)
    + goto out_put_mm;
    +
    hold_task_mempolicy(priv);

    for (vma = priv->mm->mmap; vma; vma = vma->vm_next) {
    @@ -845,8 +848,9 @@ static int show_smaps_rollup(struct seq_file *m, void *v)

    release_task_mempolicy(priv);
    up_read(&mm->mmap_sem);
    - mmput(mm);

    +out_put_mm:
    + mmput(mm);
    out_put_task:
    put_task_struct(priv->task);
    priv->task = NULL;
    --
    2.20.1
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