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btrfs: send: check for dead send root under critical section

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We're checking if the send root is dead without the protection of the
root's root_item_lock spinlock, which is what protects the root's flags.
The inverse, setting the dead flag on a root, is done under the protection
of that lock, at btrfs_delete_subvolume(). Also checking and updating the
root's send_in_progress counter is supposed to be done in the same
critical section as checking for or setting the root dead flag, so that
these operations are done atomically as a single step (which is correctly
done by btrfs_delete_subvolume()).

So fix this by checking if the send root is dead in the same critical
section that updates the send_in_progress counter, which is protected by
the root's root_item_lock spinlock.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Filipe Manana
2024-11-06 10:32:09 +00:00
committed by David Sterba
parent 722d343f12
commit dc058f5fda
1 changed files with 8 additions and 9 deletions
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17
fs/btrfs/send.c
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@@ -8125,6 +8125,14 @@ long btrfs_ioctl_send(struct btrfs_inode *inode, const struct btrfs_ioctl_send_a
* making it RW. This also protects against deletion.
*/
spin_lock(&send_root->root_item_lock);
/*
* Unlikely but possible, if the subvolume is marked for deletion but
* is slow to remove the directory entry, send can still be started.
*/
if (btrfs_root_dead(send_root)) {
spin_unlock(&send_root->root_item_lock);
return -EPERM;
}
if (btrfs_root_readonly(send_root) && send_root->dedupe_in_progress) {
dedupe_in_progress_warn(send_root);
spin_unlock(&send_root->root_item_lock);
@@ -8207,15 +8215,6 @@ long btrfs_ioctl_send(struct btrfs_inode *inode, const struct btrfs_ioctl_send_a
}
sctx->send_root = send_root;
/*
* Unlikely but possible, if the subvolume is marked for deletion but
* is slow to remove the directory entry, send can still be started
*/
if (btrfs_root_dead(sctx->send_root)) {
ret = -EPERM;
goto out;
}
sctx->clone_roots_cnt = arg->clone_sources_count;
if (sctx->proto >= 2) {