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    Subject[PATCH AUTOSEL 5.2 164/171] proc: use down_read_killable mmap_sem for /proc/pid/pagemap
    Date
    From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

    [ Upstream commit ad80b932c57d85fd6377f97f359b025baf179a87 ]

    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/156007493638.3335.4872164955523928492.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 | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
    index 4d9a8e72d91f..1d9c63cd8a3c 100644
    --- a/fs/proc/task_mmu.c
    +++ b/fs/proc/task_mmu.c
    @@ -1543,7 +1543,9 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
    /* overflow ? */
    if (end < start_vaddr || end > end_vaddr)
    end = end_vaddr;
    - down_read(&mm->mmap_sem);
    + ret = down_read_killable(&mm->mmap_sem);
    + if (ret)
    + goto out_free;
    ret = walk_page_range(start_vaddr, end, &pagemap_walk);
    up_read(&mm->mmap_sem);
    start_vaddr = end;
    --
    2.20.1
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