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

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

[Yang Shi]

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

Re: [v2 UPDATE PATCH] mm: shmem: don't truncate page if memory failure happens

[Yang Shi]

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
>

Re: [v2 UPDATE PATCH] mm: shmem: don't truncate page if memory failure happens

[Linus Torvalds]

On Thu, Nov 18, 2021 at 10:55 AM Yang Shi <shy828301@gmail.com> wrote:
>
> Does this version look good to you? Would you please consider to apply
> this to -rc2? Or you prefer to get it from Andrew?

I don't see anything wrong, but yes, I'd prefer this to go through the
-mm tree and get at least that minimal testing (and maybe extra eyes)

         Linus

Re: [v2 UPDATE PATCH] mm: shmem: don't truncate page if memory failure happens

[Yang Shi]

On Sat, Nov 20, 2021 at 2:13 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Thu, Nov 18, 2021 at 10:55 AM Yang Shi <shy828301@gmail.com> wrote:
> >
> > Does this version look good to you? Would you please consider to apply
> > this to -rc2? Or you prefer to get it from Andrew?
>
> I don't see anything wrong, but yes, I'd prefer this to go through the
> -mm tree and get at least that minimal testing (and maybe extra eyes)

Thanks, it has been in the -mm tree.

>
>          Linus