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SubjectRe: [PATCH v2 6/6] fs/proc/kcore: use page_offline_(freeze|thaw)
On Fri, May 14, 2021 at 07:22:47PM +0200, David Hildenbrand wrote:
> Let's properly synchronize with drivers that set PageOffline().
> Unfreeze/thaw every now and then, so drivers that want to set PageOffline()
> can make progress.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Acked-by: Mike Rapoport <rppt@linux.ibm.com>

> ---
> fs/proc/kcore.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index 92ff1e4436cb..982e694aae77 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -313,6 +313,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> {
> char *buf = file->private_data;
> size_t phdrs_offset, notes_offset, data_offset;
> + size_t page_offline_frozen = 1;
> size_t phdrs_len, notes_len;
> struct kcore_list *m;
> size_t tsz;
> @@ -322,6 +323,11 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> int ret = 0;
>
> down_read(&kclist_lock);
> + /*
> + * Don't race against drivers that set PageOffline() and expect no
> + * further page access.
> + */
> + page_offline_freeze();
>
> get_kcore_size(&nphdr, &phdrs_len, &notes_len, &data_offset);
> phdrs_offset = sizeof(struct elfhdr);
> @@ -480,6 +486,12 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> }
> }
>
> + if (page_offline_frozen++ % MAX_ORDER_NR_PAGES == 0) {
> + page_offline_thaw();
> + cond_resched();
> + page_offline_freeze();
> + }
> +
> if (&m->list == &kclist_head) {
> if (clear_user(buffer, tsz)) {
> ret = -EFAULT;
> @@ -565,6 +577,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> }
>
> out:
> + page_offline_thaw();
> up_read(&kclist_lock);
> if (ret)
> return ret;
> --
> 2.31.1
>

--
Sincerely yours,
Mike.

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