erofs: initialized fields can only be observed after bit is set

Currently, although set_bit() & test_bit() pairs are used as a fast-
path for initialized configurations. However, these atomic ops are
actually relaxed forms. Instead, load-acquire & store-release form is
needed to make sure uninitialized fields won't be observed in advance
here (yet no such corresponding bitops so use full barriers instead.)

Link: https://lore.kernel.org/r/20210209130618.15838-1-hsiangkao@aol.com
Fixes: 62dc45979f3f ("staging: erofs: fix race of initializing xattrs of a inode at the same time")
Fixes: 152a333a5895 ("staging: erofs: add compacted compression indexes support")
Cc: <stable@vger.kernel.org> # 5.3+
Reported-by: Huang Jianan <huangjianan@oppo.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
index 5bde77d708524466391289d4bc39cf1b8254ec3b..47314a26767a844fb016b1b8ebe435c014f4a1ea 100644 (file)
--- a/fs/erofs/xattr.c
+++ b/fs/erofs/xattr.c
@@ -48,8 +48,14 @@ static int init_inode_xattrs(struct inode *inode)
        int ret = 0;
 
        /* the most case is that xattrs of this inode are initialized. */
-       if (test_bit(EROFS_I_EA_INITED_BIT, &vi->flags))
+       if (test_bit(EROFS_I_EA_INITED_BIT, &vi->flags)) {
+               /*
+                * paired with smp_mb() at the end of the function to ensure
+                * fields will only be observed after the bit is set.
+                */
+               smp_mb();
                return 0;
+       }
 
        if (wait_on_bit_lock(&vi->flags, EROFS_I_BL_XATTR_BIT, TASK_KILLABLE))
                return -ERESTARTSYS;
@@ -137,6 +143,8 @@ static int init_inode_xattrs(struct inode *inode)
        }
        xattr_iter_end(&it, atomic_map);
 
+       /* paired with smp_mb() at the beginning of the function. */
+       smp_mb();
        set_bit(EROFS_I_EA_INITED_BIT, &vi->flags);
 
 out_unlock:

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index ae325541884e3b44332bba1cdf1d357e55e510f6..14d2de35110ccd25c005ac96865c660c06d43f44 100644 (file)
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -36,8 +36,14 @@ static int z_erofs_fill_inode_lazy(struct inode *inode)
        void *kaddr;
        struct z_erofs_map_header *h;
 
-       if (test_bit(EROFS_I_Z_INITED_BIT, &vi->flags))
+       if (test_bit(EROFS_I_Z_INITED_BIT, &vi->flags)) {
+               /*
+                * paired with smp_mb() at the end of the function to ensure
+                * fields will only be observed after the bit is set.
+                */
+               smp_mb();
                return 0;
+       }
 
        if (wait_on_bit_lock(&vi->flags, EROFS_I_BL_Z_BIT, TASK_KILLABLE))
                return -ERESTARTSYS;
@@ -83,6 +89,8 @@ static int z_erofs_fill_inode_lazy(struct inode *inode)
 
        vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits +
                                        ((h->h_clusterbits >> 5) & 7);
+       /* paired with smp_mb() at the beginning of the function */
+       smp_mb();
        set_bit(EROFS_I_Z_INITED_BIT, &vi->flags);
 unmap_done:
        kunmap_atomic(kaddr);