xfs: use WRITE_ONCE/READ_ONCE for m_errortag

There is no synchronization for updating m_errortag, which is fine as
it's just a debug tool.  It would still be nice to fully avoid the
theoretical case of torn values, so use WRITE_ONCE and READ_ONCE to
access the members.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

diff --git a/fs/xfs/xfs_error.c b/fs/xfs/xfs_error.c
index a6f160a4d0e906c0e76bcda4e017ef21859320ce..53704f1ed7910b56f3afd862afe22021e328f90e 100644 (file)
--- a/fs/xfs/xfs_error.c
+++ b/fs/xfs/xfs_error.c
@@ -50,17 +50,18 @@ xfs_errortag_attr_store(
 {
        struct xfs_mount        *mp = to_mp(kobject);
        unsigned int            error_tag = to_attr(attr)->tag;
+       unsigned int            val;
        int                     ret;
 
        if (strcmp(buf, "default") == 0) {
-               mp->m_errortag[error_tag] =
-                       xfs_errortag_random_default[error_tag];
+               val = xfs_errortag_random_default[error_tag];
        } else {
-               ret = kstrtouint(buf, 0, &mp->m_errortag[error_tag]);
+               ret = kstrtouint(buf, 0, &val);
                if (ret)
                        return ret;
        }
 
+       WRITE_ONCE(mp->m_errortag[error_tag], val);
        return count;
 }
 
@@ -71,9 +72,9 @@ xfs_errortag_attr_show(
        char                    *buf)
 {
        struct xfs_mount        *mp = to_mp(kobject);
-       unsigned int            error_tag = to_attr(attr)->tag;
 
-       return snprintf(buf, PAGE_SIZE, "%u\n", mp->m_errortag[error_tag]);
+       return snprintf(buf, PAGE_SIZE, "%u\n",
+                       READ_ONCE(mp->m_errortag[to_attr(attr)->tag]));
 }
 
 static const struct sysfs_ops xfs_errortag_sysfs_ops = {
@@ -134,7 +135,7 @@ xfs_errortag_test(
 {
        unsigned int            randfactor;
 
-       randfactor = mp->m_errortag[error_tag];
+       randfactor = READ_ONCE(mp->m_errortag[error_tag]);
        if (!randfactor || get_random_u32_below(randfactor))
                return false;
 
@@ -151,7 +152,7 @@ xfs_errortag_delay(
        int                     line,
        unsigned int            error_tag)
 {
-       unsigned int            delay = mp->m_errortag[error_tag];
+       unsigned int            delay = READ_ONCE(mp->m_errortag[error_tag]);
 
        might_sleep();
 
@@ -183,7 +184,8 @@ xfs_errortag_add(
                break;
        }
 
-       mp->m_errortag[error_tag] = xfs_errortag_random_default[error_tag];
+       WRITE_ONCE(mp->m_errortag[error_tag],
+                  xfs_errortag_random_default[error_tag]);
        return 0;
 }
 
@@ -191,7 +193,10 @@ int
 xfs_errortag_clearall(
        struct xfs_mount        *mp)
 {
-       memset(mp->m_errortag, 0, sizeof(unsigned int) * XFS_ERRTAG_MAX);
+       unsigned int            i;
+
+       for (i = 0; i < XFS_ERRTAG_MAX; i++)
+               WRITE_ONCE(mp->m_errortag[i], 0);
        return 0;
 }
 #endif /* DEBUG */