We can access and check metacopy flag outside ovl_inode->lock. IOW, say
a file was meta copied up in the past and it has metacopy flag set. Now
a data copy up operation in progress. Say another thread reads state of
this flag and if flag clearing is visible before file has been fully
copied up, that can cause problems.
CPU1 CPU2
ovl_copy_up_flags() acquire(oi->lock)
ovl_dentry_needs_data_copy_up() ovl_copy_up_data_inode()
ovl_test_metacopy_flag() ovl_copy_up_data()
ovl_clear_metacopy_flag()
release(oi->lock)
Say CPU2 is copying up data and in the end clears metacopy flag. But if
CPU1 perceives clearing of metacopy before actual data copy up operation
being finished, that can become a problem. We want this clearing of flag
to be visible only if all previous write operations have finished.
Hence this patch introduces smp_wmb() on metacopy flag set/clear operation
and smp_rmb() on metacopy flag test operation.
May be some other lock or barrier is already covering it. But I am not sure
what that is and is it obvious enough that we will not break it in future.
So hence trying to be safe here and introducing barriers explicitly for
metacopy bit.
Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
---
fs/overlayfs/copy_up.c | 9 +++------
fs/overlayfs/overlayfs.h | 3 +++
fs/overlayfs/util.c | 23 ++++++++++++++++++++++-
3 files changed, 28 insertions(+), 7 deletions(-)
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 682852a78163..b10269b80803 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -465,8 +465,7 @@ static int ovl_copy_up_data_inode(struct ovl_copy_up_ctx *c)
if (err)
return err;
- smp_wmb();
- ovl_clear_flag(OVL_METACOPY, d_inode(c->dentry));
+ ovl_clear_metacopy_flag(d_inode(c->dentry));
return err;
}
@@ -564,10 +563,8 @@ static int ovl_copy_up_locked(struct ovl_copy_up_ctx *c)
goto out_cleanup;
ovl_inode_update(d_inode(c->dentry), newdentry);
- if (c->metadata_only) {
- smp_wmb();
- ovl_set_flag(OVL_METACOPY, d_inode(c->dentry));
- }
+ if (c->metadata_only)
+ ovl_set_metacopy_flag(d_inode(c->dentry));
out:
dput(temp);
return err;
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 773f5ad75729..df3f513de3cc 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -234,6 +234,9 @@ int ovl_set_impure(struct dentry *dentry, struct dentry *upperdentry);
void ovl_set_flag(unsigned long flag, struct inode *inode);
void ovl_clear_flag(unsigned long flag, struct inode *inode);
bool ovl_test_flag(unsigned long flag, struct inode *inode);
+void ovl_set_metacopy_flag(struct inode *inode);
+void ovl_clear_metacopy_flag(struct inode *inode);
+bool ovl_test_metacopy_flag(struct inode *inode);
bool ovl_inuse_trylock(struct dentry *dentry);
void ovl_inuse_unlock(struct dentry *dentry);
int ovl_nlink_start(struct dentry *dentry, bool *locked);
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 91c542d1a39d..000f78b92a72 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -227,6 +227,27 @@ void ovl_dentry_set_upper_alias(struct dentry *dentry)
oe->has_upper = true;
}
+bool ovl_test_metacopy_flag(struct inode *inode)
+{
+ /* Pairs with smp_wmb() in ovl_set_metacopy_flag() */
+ smp_rmb();
+ return ovl_test_flag(OVL_METACOPY, inode);
+}
+
+void ovl_set_metacopy_flag(struct inode *inode)
+{
+ /* Pairs with smp_rmb() in ovl_test_metacopy_flag() */
+ smp_wmb();
+ ovl_set_flag(OVL_METACOPY, inode);
+}
+
+void ovl_clear_metacopy_flag(struct inode *inode)
+{
+ /* Pairs with smp_rmb() in ovl_test_metacopy_flag() */
+ smp_wmb();
+ ovl_clear_flag(OVL_METACOPY, inode);
+}
+
bool ovl_dentry_needs_data_copy_up(struct dentry *dentry, int flags) {
if (!S_ISREG(d_inode(dentry)->i_mode))
return false;
@@ -237,7 +258,7 @@ bool ovl_dentry_needs_data_copy_up(struct dentry *dentry, int flags) {
if (!(OPEN_FMODE(flags) & FMODE_WRITE))
return false;
- if (!ovl_test_flag(OVL_METACOPY, d_inode(dentry)))
+ if (!ovl_test_metacopy_flag(d_inode(dentry)))
return false;
return true;
--
2.13.5
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