New subject: [f2fs-dev] [PATCH] f2fs: remove i_xattr_sem to avoid deadlock and fix the original issue

13 Jun 2023

This reverts commit 27161f13e3c3 "f2fs: avoid race in between read xattr & write xattr".
That introduced a deadlock case:
Thread #1:
[122554.641906][   T92]  f2fs_getxattr+0xd4/0x5fc
    -> waiting for f2fs_down_read(&F2FS_I(inode)->i_xattr_sem);
[122554.641927][   T92]  __f2fs_get_acl+0x50/0x284
[122554.641948][   T92]  f2fs_init_acl+0x84/0x54c
[122554.641969][   T92]  f2fs_init_inode_metadata+0x460/0x5f0
[122554.641990][   T92]  f2fs_add_inline_entry+0x11c/0x350
    -> Locked dir->inode_page by f2fs_get_node_page()
[122554.642009][   T92]  f2fs_do_add_link+0x100/0x1e4
[122554.642025][   T92]  f2fs_create+0xf4/0x22c
[122554.642047][   T92]  vfs_create+0x130/0x1f4
Thread #2:
[123996.386358][   T92]  __get_node_page+0x8c/0x504
    -> waiting for dir->inode_page lock
[123996.386383][   T92]  read_all_xattrs+0x11c/0x1f4
[123996.386405][   T92]  __f2fs_setxattr+0xcc/0x528
[123996.386424][   T92]  f2fs_setxattr+0x158/0x1f4
    -> f2fs_down_write(&F2FS_I(inode)->i_xattr_sem);
[123996.386443][   T92]  __f2fs_set_acl+0x328/0x430
[123996.386618][   T92]  f2fs_set_acl+0x38/0x50
[123996.386642][   T92]  posix_acl_chmod+0xc8/0x1c8
[123996.386669][   T92]  f2fs_setattr+0x5e0/0x6bc
[123996.386689][   T92]  notify_change+0x4d8/0x580
[123996.386717][   T92]  chmod_common+0xd8/0x184
[123996.386748][   T92]  do_fchmodat+0x60/0x124
[123996.386766][   T92]  __arm64_sys_fchmodat+0x28/0x3c
Let's take a look at the original issue back.
Thread A:                                       Thread B:
-f2fs_getxattr
   -lookup_all_xattrs
      -xnid = F2FS_I(inode)->i_xattr_nid;
                                                -f2fs_setxattr
                                                    -__f2fs_setxattr
                                                        -write_all_xattrs
                                                            -truncate_xattr_node
                                                                  ...  ...
                                                -write_checkpoint
                                                                  ...  ...
                                                -alloc_nid   <- nid reuse
          -get_node_page
              -f2fs_bug_on  <- nid != node_footer->nid
I think we don't need to truncate xattr pages eagerly which introduces lots of
data races without big benefits.
Cc: stable@vger.kernel.org
Signed-off-by: Jaegeuk Kim jaegeuk@kernel.org
---
 fs/f2fs/f2fs.h  |  1 -
 fs/f2fs/super.c |  1 -
 fs/f2fs/xattr.c | 31 ++++++++-----------------------
 3 files changed, 8 insertions(+), 25 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 3f5b161dd743..7b9af2d51656 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -838,7 +838,6 @@ struct f2fs_inode_info {
/* avoid racing between foreground op and gc */
    struct f2fs_rwsem i_gc_rwsem[2];
-	struct f2fs_rwsem i_xattr_sem; /* avoid racing between reading and changing EAs */
int i_extra_isize;		/* size of extra space located in i_addr */
    kprojid_t i_projid;		/* id for project quota */
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 1b2c788ed80d..c917fa771f0e 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1418,7 +1418,6 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb)
    INIT_LIST_HEAD(&fi->gdirty_list);
    init_f2fs_rwsem(&fi->i_gc_rwsem[READ]);
    init_f2fs_rwsem(&fi->i_gc_rwsem[WRITE]);
-	init_f2fs_rwsem(&fi->i_xattr_sem);
/* Will be used by directory only */
    fi->i_dir_level = F2FS_SB(sb)->dir_level;
diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
index 213805d3592c..bdc8a55085a2 100644
--- a/fs/f2fs/xattr.c
+++ b/fs/f2fs/xattr.c
@@ -433,7 +433,7 @@ static inline int write_all_xattrs(struct inode *inode, __u32 hsize,
 {
    struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
    size_t inline_size = inline_xattr_size(inode);
-	struct page *in_page = NULL;
+	struct page *in_page = ipage;
    void *xattr_addr;
    void *inline_addr = NULL;
    struct page *xpage;
@@ -446,29 +446,19 @@ static inline int write_all_xattrs(struct inode *inode, __u32 hsize,
/* write to inline xattr */
    if (inline_size) {
-		if (ipage) {
-			inline_addr = inline_xattr_addr(inode, ipage);
-		} else {
+		if (!in_page) {
    		in_page = f2fs_get_node_page(sbi, inode->i_ino);
    		if (IS_ERR(in_page)) {
    			f2fs_alloc_nid_failed(sbi, new_nid);
    			return PTR_ERR(in_page);
    		}
-			inline_addr = inline_xattr_addr(inode, in_page);
    	}
+		inline_addr = inline_xattr_addr(inode, in_page);
-		f2fs_wait_on_page_writeback(ipage ? ipage : in_page,
-							NODE, true, true);
-		/* no need to use xattr node block */
+		f2fs_wait_on_page_writeback(in_page, NODE, true, true);
    	if (hsize <= inline_size) {
-			err = f2fs_truncate_xattr_node(inode);
-			f2fs_alloc_nid_failed(sbi, new_nid);
-			if (err) {
-				f2fs_put_page(in_page, 1);
-				return err;
-			}
    		memcpy(inline_addr, txattr_addr, inline_size);
-			set_page_dirty(ipage ? ipage : in_page);
+			set_page_dirty(in_page);
    		goto in_page_out;
    	}
    }
@@ -502,12 +492,13 @@ static inline int write_all_xattrs(struct inode *inode, __u32 hsize,
    memcpy(xattr_addr, txattr_addr + inline_size, VALID_XATTR_BLOCK_SIZE);
if (inline_size)
-		set_page_dirty(ipage ? ipage : in_page);
+		set_page_dirty(in_page);
    set_page_dirty(xpage);
f2fs_put_page(xpage, 1);
 in_page_out:
-	f2fs_put_page(in_page, 1);
+	if (in_page != ipage)
+		f2fs_put_page(in_page, 1);
    return err;
 }
@@ -528,10 +519,8 @@ int f2fs_getxattr(struct inode *inode, int index, const char *name,
    if (len > F2FS_NAME_LEN)
    	return -ERANGE;
-	f2fs_down_read(&F2FS_I(inode)->i_xattr_sem);
    error = lookup_all_xattrs(inode, ipage, index, len, name,
    			&entry, &base_addr, &base_size, &is_inline);
-	f2fs_up_read(&F2FS_I(inode)->i_xattr_sem);
    if (error)
    	return error;
@@ -565,9 +554,7 @@ ssize_t f2fs_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
    int error;
    size_t rest = buffer_size;
-	f2fs_down_read(&F2FS_I(inode)->i_xattr_sem);
    error = read_all_xattrs(inode, NULL, &base_addr);
-	f2fs_up_read(&F2FS_I(inode)->i_xattr_sem);
    if (error)
    	return error;
@@ -794,9 +781,7 @@ int f2fs_setxattr(struct inode *inode, int index, const char *name,
    f2fs_balance_fs(sbi, true);
f2fs_lock_op(sbi);
-	f2fs_down_write(&F2FS_I(inode)->i_xattr_sem);
    err = __f2fs_setxattr(inode, index, name, value, size, ipage, flags);
-	f2fs_up_write(&F2FS_I(inode)->i_xattr_sem);
    f2fs_unlock_op(sbi);
f2fs_update_time(sbi, REQ_TIME);
-- 
2.41.0.162.gfafddb0af9-goog


    