Revert "mm: shmem: don't truncate page if memory failure happens"

This reverts commit b9d02f1bdd98f38e6e5ecacc9786a8f58f3f8b2c.

The error handling of that patch was fundamentally broken, and it needs
to be entirely re-done.

For example, in shmem_write_begin() it would call shmem_getpage(), then
ignore the error return from that, and look at the page pointer contents
instead.

And in shmem_read_mapping_page_gfp(), the patch tested PageHWPoison() on
a page pointer that two lines earlier had potentially been set as an
error pointer.

These issues could be individually fixed, but when it has this many
issues, I'm just reverting it instead of waiting for fixes.

Link: https://lore.kernel.org/linux-mm/[e-mail]/
Reported-by: Ajay Garg <[e-mail]>
Reported-by: Jens Axboe <[e-mail]>
Cc: Yang Shi <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/memory-failure.c

···
 #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"
 
···
 {
 	int ret;
 	struct address_space *mapping;
-	bool extra_pins;
 
 	delete_from_lru_cache(p);
 
···
 	}
 
 	/*
-	 * 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;
 }

mm/shmem.c

···
 	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 |
···
 			return -EPERM;
 	}
 
-	ret = shmem_getpage(inode, index, pagep, SGP_WRITE);
-
-	if (*pagep && PageHWPoison(*pagep)) {
-		unlock_page(*pagep);
-		put_page(*pagep);
-		ret = -EIO;
-	}
-
-	return ret;
+	return shmem_getpage(inode, index, pagep, SGP_WRITE);
 }
 
 static int
···
 			if (sgp == SGP_CACHE)
 				set_page_dirty(page);
 			unlock_page(page);
-
-			if (PageHWPoison(page)) {
-				put_page(page);
-				error = -EIO;
-				break;
-			}
 		}
 
 		/*
···
 		page = find_get_page(inode->i_mapping, 0);
 		if (!page)
 			return ERR_PTR(-ECHILD);
-		if (PageHWPoison(page) ||
-		    !PageUptodate(page)) {
+		if (!PageUptodate(page)) {
 			put_page(page);
 			return ERR_PTR(-ECHILD);
 		}
···
 		error = shmem_getpage(inode, 0, &page, SGP_READ);
 		if (error)
 			return ERR_PTR(error);
-		if (page && PageHWPoison(page)) {
-			unlock_page(page);
-			put_page(page);
-			return ERR_PTR(-ECHILD);
-		}
 		unlock_page(page);
 	}
 	set_delayed_call(done, shmem_put_link, page);
···
 	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,
···
 #ifdef CONFIG_MIGRATION
 	.migratepage	= migrate_page,
 #endif
-	.error_remove_page = shmem_error_remove_page,
+	.error_remove_page = generic_error_remove_page,
 };
 EXPORT_SYMBOL(shmem_aops);
 
···
 		page = ERR_PTR(error);
 	else
 		unlock_page(page);
-
-	if (PageHWPoison(page))
-		page = ERR_PTR(-EIO);
-
 	return page;
 #else
 	/*

mm/userfaultfd.c

···
 		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)