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SubjectRe: [v2 UPDATE PATCH] mm: shmem: don't truncate page if memory failure happens
Hi Linus,

Does this version look good to you? Would you please consider to apply
this to -rc2? Or you prefer to get it from Andrew?

Thanks,
Yang

On Tue, Nov 16, 2021 at 11:32 AM Yang Shi <shy828301@gmail.com> wrote:
>
> The current behavior of memory failure is to truncate the page cache
> regardless of dirty or clean. If the page is dirty the later access
> will get the obsolete data from disk without any notification to the
> users. This may cause silent data loss. It is even worse for shmem
> since shmem is in-memory filesystem, truncating page cache means
> discarding data blocks. The later read would return all zero.
>
> The right approach is to keep the corrupted page in page cache, any
> later access would return error for syscalls or SIGBUS for page fault,
> until the file is truncated, hole punched or removed. The regular
> storage backed filesystems would be more complicated so this patch is
> focused on shmem. This also unblock the support for soft offlining
> shmem THP.
>
> [arnd@arndb.de: fix uninitialized variable use in me_pagecache_clean()]
> Link: https://lkml.kernel.org/r/20211022064748.4173718-1-arnd@kernel.org
> [Fix invalid pointer dereference in shmem_read_mapping_page_gfp() with a
> slight different implementation from what Ajay Garg <ajaygargnsit@gmail.com>
> and Muchun Song <songmuchun@bytedance.com> proposed and reworked the
> error handling of shmem_write_begin() suggested by Linus]
> Link: https://lore.kernel.org/linux-mm/20211111084617.6746-1-ajaygargnsit@gmail.com/
>
> Link: https://lkml.kernel.org/r/20211020210755.23964-6-shy828301@gmail.com
> Signed-off-by: Yang Shi <shy828301@gmail.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Ajay Garg <ajaygargnsit@gmail.com>
> Cc: Muchun Song <songmuchun@bytedance.com>
> ---
> v2: Incorporated the suggestions from Willy.
> v1: Fixed pointer dereference oops reported by Ajay Garg and reworked the
> error handling of shmem_write_begin() suggested by Linus.
>
> mm/memory-failure.c | 14 ++++++++++---
> mm/shmem.c | 51 +++++++++++++++++++++++++++++++++++++++------
> mm/userfaultfd.c | 5 +++++
> 3 files changed, 61 insertions(+), 9 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 07c875fdeaf0..f64ebb6226cb 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -58,6 +58,7 @@
> #include <linux/ratelimit.h>
> #include <linux/page-isolation.h>
> #include <linux/pagewalk.h>
> +#include <linux/shmem_fs.h>
> #include "internal.h"
> #include "ras/ras_event.h"
>
> @@ -867,6 +868,7 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
> {
> int ret;
> struct address_space *mapping;
> + bool extra_pins;
>
> delete_from_lru_cache(p);
>
> @@ -895,18 +897,24 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p)
> goto out;
> }
>
> + /*
> + * The shmem page is kept in page cache instead of truncating
> + * so is expected to have an extra refcount after error-handling.
> + */
> + extra_pins = shmem_mapping(mapping);
> +
> /*
> * Truncation is a bit tricky. Enable it per file system for now.
> *
> * Open: to take i_rwsem or not for this? Right now we don't.
> */
> ret = truncate_error_page(p, page_to_pfn(p), mapping);
> + if (has_extra_refcount(ps, p, extra_pins))
> + ret = MF_FAILED;
> +
> out:
> unlock_page(p);
>
> - if (has_extra_refcount(ps, p, false))
> - ret = MF_FAILED;
> -
> return ret;
> }
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index dc038ce78700..2ba64918132b 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -2456,6 +2456,7 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
> struct inode *inode = mapping->host;
> struct shmem_inode_info *info = SHMEM_I(inode);
> pgoff_t index = pos >> PAGE_SHIFT;
> + int ret = 0;
>
> /* i_rwsem is held by caller */
> if (unlikely(info->seals & (F_SEAL_GROW |
> @@ -2466,7 +2467,19 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
> return -EPERM;
> }
>
> - return shmem_getpage(inode, index, pagep, SGP_WRITE);
> + ret = shmem_getpage(inode, index, pagep, SGP_WRITE);
> +
> + if (ret)
> + return ret;
> +
> + if (PageHWPoison(*pagep)) {
> + unlock_page(*pagep);
> + put_page(*pagep);
> + *pagep = NULL;
> + return -EIO;
> + }
> +
> + return 0;
> }
>
> static int
> @@ -2553,6 +2566,12 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> if (sgp == SGP_CACHE)
> set_page_dirty(page);
> unlock_page(page);
> +
> + if (PageHWPoison(page)) {
> + put_page(page);
> + error = -EIO;
> + break;
> + }
> }
>
> /*
> @@ -3092,7 +3111,8 @@ static const char *shmem_get_link(struct dentry *dentry,
> page = find_get_page(inode->i_mapping, 0);
> if (!page)
> return ERR_PTR(-ECHILD);
> - if (!PageUptodate(page)) {
> + if (PageHWPoison(page) ||
> + !PageUptodate(page)) {
> put_page(page);
> return ERR_PTR(-ECHILD);
> }
> @@ -3100,6 +3120,13 @@ static const char *shmem_get_link(struct dentry *dentry,
> error = shmem_getpage(inode, 0, &page, SGP_READ);
> if (error)
> return ERR_PTR(error);
> + if (!page)
> + return ERR_PTR(-ECHILD);
> + if (PageHWPoison(page)) {
> + unlock_page(page);
> + put_page(page);
> + return ERR_PTR(-ECHILD);
> + }
> unlock_page(page);
> }
> set_delayed_call(done, shmem_put_link, page);
> @@ -3750,6 +3777,13 @@ static void shmem_destroy_inodecache(void)
> kmem_cache_destroy(shmem_inode_cachep);
> }
>
> +/* Keep the page in page cache instead of truncating it */
> +static int shmem_error_remove_page(struct address_space *mapping,
> + struct page *page)
> +{
> + return 0;
> +}
> +
> const struct address_space_operations shmem_aops = {
> .writepage = shmem_writepage,
> .set_page_dirty = __set_page_dirty_no_writeback,
> @@ -3760,7 +3794,7 @@ const struct address_space_operations shmem_aops = {
> #ifdef CONFIG_MIGRATION
> .migratepage = migrate_page,
> #endif
> - .error_remove_page = generic_error_remove_page,
> + .error_remove_page = shmem_error_remove_page,
> };
> EXPORT_SYMBOL(shmem_aops);
>
> @@ -4168,9 +4202,14 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
> error = shmem_getpage_gfp(inode, index, &page, SGP_CACHE,
> gfp, NULL, NULL, NULL);
> if (error)
> - page = ERR_PTR(error);
> - else
> - unlock_page(page);
> + return ERR_PTR(error);
> +
> + unlock_page(page);
> + if (PageHWPoison(page)) {
> + put_page(page);
> + return ERR_PTR(-EIO);
> + }
> +
> return page;
> #else
> /*
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index ac6f036298cd..0780c2a57ff1 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -232,6 +232,11 @@ static int mcontinue_atomic_pte(struct mm_struct *dst_mm,
> goto out;
> }
>
> + if (PageHWPoison(page)) {
> + ret = -EIO;
> + goto out_release;
> + }
> +
> ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
> page, false, wp_copy);
> if (ret)
> --
> 2.26.2
>

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