On Sun, Jun 09, 2019 at 01:09:00PM +0300, Konstantin Khlebnikov wrote:
> Do not stuck forever if something wrong.
> Killable lock allows to cleanup stuck tasks and simplifies investigation.
This patch breaks the CRIU project, because stat() returns EINTR instead
of ENOENT:
[root@fc24 criu]# stat /proc/self/map_files/0-0
stat: cannot stat '/proc/self/map_files/0-0': Interrupted system call
Here is one inline comment with the fix for this issue.
>
> It seems ->d_revalidate() could return any error (except ECHILD) to
> abort validation and pass error as result of lookup sequence.
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> Reviewed-by: Roman Gushchin <guro@xxxxxx>
> Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
> Reviewed-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
It was nice to see all four of you in one place :).
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> fs/proc/base.c | 27 +++++++++++++++++++++------
> 1 file changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 9c8ca6cd3ce4..515ab29c2adf 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 +2113,10 @@ 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 +2127,7 @@ 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 +2170,12 @@ 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;
>
