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    Subject[PATCH AUTOSEL 5.2 166/171] proc: use down_read_killable mmap_sem for /proc/pid/map_files
    Date
    From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

    [ Upstream commit cd9e2bb8271c971d9f37c722be2616c7f8ba0664 ]

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

    It seems ->d_revalidate() could return any error (except ECHILD) to abort
    validation and pass error as result of lookup sequence.

    [akpm@linux-foundation.org: fix proc_map_files_lookup() return value, per Andrei]
    Link: http://lkml.kernel.org/r/156007493995.3335.9595044802115356911.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/base.c | 28 ++++++++++++++++++++++------
    1 file changed, 22 insertions(+), 6 deletions(-)

    diff --git a/fs/proc/base.c b/fs/proc/base.c
    index 255f6754c70d..03517154fe0f 100644
    --- a/fs/proc/base.c
    +++ b/fs/proc/base.c
    @@ -1962,9 +1962,12 @@ static int map_files_d_revalidate(struct dentry *dentry, unsigned int flags)
    goto out;

    if (!dname_to_vma_addr(dentry, &vm_start, &vm_end)) {
    - down_read(&mm->mmap_sem);
    - exact_vma_exists = !!find_exact_vma(mm, vm_start, vm_end);
    - up_read(&mm->mmap_sem);
    + status = down_read_killable(&mm->mmap_sem);
    + if (!status) {
    + exact_vma_exists = !!find_exact_vma(mm, vm_start,
    + vm_end);
    + up_read(&mm->mmap_sem);
    + }
    }

    mmput(mm);
    @@ -2010,8 +2013,11 @@ static int map_files_get_link(struct dentry *dentry, struct path *path)
    if (rc)
    goto out_mmput;

    + rc = down_read_killable(&mm->mmap_sem);
    + if (rc)
    + goto out_mmput;
    +
    rc = -ENOENT;
    - down_read(&mm->mmap_sem);
    vma = find_exact_vma(mm, vm_start, vm_end);
    if (vma && vma->vm_file) {
    *path = vma->vm_file->f_path;
    @@ -2107,7 +2113,11 @@ static struct dentry *proc_map_files_lookup(struct inode *dir,
    if (!mm)
    goto out_put_task;

    - down_read(&mm->mmap_sem);
    + result = ERR_PTR(-EINTR);
    + if (down_read_killable(&mm->mmap_sem))
    + goto out_put_mm;
    +
    + result = ERR_PTR(-ENOENT);
    vma = find_exact_vma(mm, vm_start, vm_end);
    if (!vma)
    goto out_no_vma;
    @@ -2118,6 +2128,7 @@ static struct dentry *proc_map_files_lookup(struct inode *dir,

    out_no_vma:
    up_read(&mm->mmap_sem);
    +out_put_mm:
    mmput(mm);
    out_put_task:
    put_task_struct(task);
    @@ -2160,7 +2171,12 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
    mm = get_task_mm(task);
    if (!mm)
    goto out_put_task;
    - down_read(&mm->mmap_sem);
    +
    + ret = down_read_killable(&mm->mmap_sem);
    + if (ret) {
    + mmput(mm);
    + goto out_put_task;
    + }

    nr_files = 0;

    --
    2.20.1
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