On Tue, Apr 08, 2025 at 09:26:10PM +0800, Zijun Hu wrote:
From: Zijun Hu quic_zijuhu@quicinc.com
configfs_symlink() returns -EEXIST under condition d_unhashed(), but the condition often means the dentry does not exist.
Fix by changing the condition to !d_unhashed().
I don't think this is quite right.
viro put this together in 351e5d869e5ac, which was a while ago. Read his comment on 351e5d869e5ac. Because I unlock the parent directory to look up the target, we can't trust our symlink dentry hasn't been changed underneath us.
* If there is now dentry->d_inode, some other inode has been put here. -EEXIST. * If the dentry was unhashed, somehow the dentry we are creating was removed from the dcache, and adding things to our dentry will at best go nowhere, and at worst dangle in space. I'm pretty sure viro returns -EEXIST because if this dentry is unhashed, some *other* dentry has entered the dcache in its place (another file type, perhaps).
If you instead check for !d_unhashed(), you're discovering our candidate dentry is still live in the dcache, which is what we expect and want.
How did you identify this as a problem? Perhaps we need a more nuanced check than d_unhashed() these days (for example, d_is_positive/negative didn't exist back then).
Thanks, Joel
PS: I enjoyed the trip down memory lane to Al reaming me quite thoroughly for this API.
Fixes: 351e5d869e5a ("configfs: fix a deadlock in configfs_symlink()") Cc: stable@vger.kernel.org Signed-off-by: Zijun Hu quic_zijuhu@quicinc.com
fs/configfs/symlink.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c index 69133ec1fac2a854241c2a08a3b48c4c2e8d5c24..cccf61fb8317d739643834e1810b7f136058f56c 100644 --- a/fs/configfs/symlink.c +++ b/fs/configfs/symlink.c @@ -193,7 +193,7 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir, if (ret) goto out_put;
- if (dentry->d_inode || d_unhashed(dentry))
- if (dentry->d_inode || !d_unhashed(dentry)) ret = -EEXIST; else ret = inode_permission(&nop_mnt_idmap, dir,
-- 2.34.1