| Message ID | 1374779620-28788-1-git-send-email-jbacik@fusionio.com (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
> -int btrfs_add_dead_root(struct btrfs_root *root) > +void btrfs_add_dead_root(struct btrfs_root *root) > { > spin_lock(&root->fs_info->trans_lock); > - list_add_tail(&root->root_list, &root->fs_info->dead_roots); > + if (list_empty(&root->root_list)) > + list_add_tail(&root->root_list, &root->fs_info->dead_roots); > spin_unlock(&root->fs_info->trans_lock); > - return 0; > } > > /* > @@ -1925,7 +1925,7 @@ int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root) > } > root = list_first_entry(&fs_info->dead_roots, > struct btrfs_root, root_list); > - list_del(&root->root_list); > + list_del_init(&root->root_list); Looking at other root_list deletions.. do we also need _del_init() in btrfs_recover_relocation() or del_fs_roots()? (Maybe for consistency and peace of mind, if nothing else?) - z -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 25 Jul 2013 15:13:40 -0400, Josef Bacik wrote: > A user reported a panic when running with autodefrag and deleting snapshots. > This is because we could end up trying to add the root to the dead roots list > twice. To fix this check to see if we are empty before adding ourselves to the > dead roots list. Thanks, > > Signed-off-by: Josef Bacik <jbacik@fusionio.com> Tested-by: Stefan Behrens <sbehrens@giantdisaster.de> The patch eliminates the crash. The question still is whether the double addition to the list is an indication for a problem and this patch just hides that there is a problem. > --- > fs/btrfs/transaction.c | 8 ++++---- > fs/btrfs/transaction.h | 2 +- > 2 files changed, 5 insertions(+), 5 deletions(-) > > diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c > index 61a5c2c..18f7e71 100644 > --- a/fs/btrfs/transaction.c > +++ b/fs/btrfs/transaction.c > @@ -983,12 +983,12 @@ static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans, > * a dirty root struct and adds it into the list of dead roots that need to > * be deleted > */ > -int btrfs_add_dead_root(struct btrfs_root *root) > +void btrfs_add_dead_root(struct btrfs_root *root) > { > spin_lock(&root->fs_info->trans_lock); > - list_add_tail(&root->root_list, &root->fs_info->dead_roots); > + if (list_empty(&root->root_list)) > + list_add_tail(&root->root_list, &root->fs_info->dead_roots); > spin_unlock(&root->fs_info->trans_lock); > - return 0; > } > > /* > @@ -1925,7 +1925,7 @@ int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root) > } > root = list_first_entry(&fs_info->dead_roots, > struct btrfs_root, root_list); > - list_del(&root->root_list); > + list_del_init(&root->root_list); > spin_unlock(&fs_info->trans_lock); > > pr_debug("btrfs: cleaner removing %llu\n", > diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h > index 005b037..defbc42 100644 > --- a/fs/btrfs/transaction.h > +++ b/fs/btrfs/transaction.h > @@ -143,7 +143,7 @@ int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid); > int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans, > struct btrfs_root *root); > > -int btrfs_add_dead_root(struct btrfs_root *root); > +void btrfs_add_dead_root(struct btrfs_root *root); > int btrfs_defrag_root(struct btrfs_root *root); > int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root); > int btrfs_commit_transaction(struct btrfs_trans_handle *trans, > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Jul 26, 2013 at 11:38:47AM +0200, Stefan Behrens wrote: > On Thu, 25 Jul 2013 15:13:40 -0400, Josef Bacik wrote: > > A user reported a panic when running with autodefrag and deleting snapshots. > > This is because we could end up trying to add the root to the dead roots list > > twice. To fix this check to see if we are empty before adding ourselves to the > > dead roots list. Thanks, > > > > Signed-off-by: Josef Bacik <jbacik@fusionio.com> > > Tested-by: Stefan Behrens <sbehrens@giantdisaster.de> > > The patch eliminates the crash. The question still is whether the double addition to the list is an indication for a problem and this patch just hides that there is a problem. This is what is happening start writing file notice it was a random write, add it to the defrag list Delete subvol evict all dentry/icache roots inode tree is empty, add to dead root process defrag inodes lookup inode based on its location and root do our defrag iput in finish_ordered_io, which removes us from the inode tree notice the inode tree is empty, add root to dead root EXPLOSION So we could probably avoid this issue by checking the root's count before we go to lookup the inode and just bailing if the used count is 0, but then if we race between looking up the root and looking up the inode we could end up in the same situation, because we'd have to check again after looking up the inode and iput there if the count was 0 and we'd be in the same mess again, though with a much smaller window. So this patch fixes the actual problem, it's not a paper over. I will fix us to not do anything if the root has been deleted since theres no sense in doing the extra work, but we'll still need this for the small window between looking up the root and looking up the inode. Thanks, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index 61a5c2c..18f7e71 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -983,12 +983,12 @@ static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans, * a dirty root struct and adds it into the list of dead roots that need to * be deleted */ -int btrfs_add_dead_root(struct btrfs_root *root) +void btrfs_add_dead_root(struct btrfs_root *root) { spin_lock(&root->fs_info->trans_lock); - list_add_tail(&root->root_list, &root->fs_info->dead_roots); + if (list_empty(&root->root_list)) + list_add_tail(&root->root_list, &root->fs_info->dead_roots); spin_unlock(&root->fs_info->trans_lock); - return 0; } /* @@ -1925,7 +1925,7 @@ int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root) } root = list_first_entry(&fs_info->dead_roots, struct btrfs_root, root_list); - list_del(&root->root_list); + list_del_init(&root->root_list); spin_unlock(&fs_info->trans_lock); pr_debug("btrfs: cleaner removing %llu\n", diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h index 005b037..defbc42 100644 --- a/fs/btrfs/transaction.h +++ b/fs/btrfs/transaction.h @@ -143,7 +143,7 @@ int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid); int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans, struct btrfs_root *root); -int btrfs_add_dead_root(struct btrfs_root *root); +void btrfs_add_dead_root(struct btrfs_root *root); int btrfs_defrag_root(struct btrfs_root *root); int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root); int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
A user reported a panic when running with autodefrag and deleting snapshots. This is because we could end up trying to add the root to the dead roots list twice. To fix this check to see if we are empty before adding ourselves to the dead roots list. Thanks, Signed-off-by: Josef Bacik <jbacik@fusionio.com> --- fs/btrfs/transaction.c | 8 ++++---- fs/btrfs/transaction.h | 2 +- 2 files changed, 5 insertions(+), 5 deletions(-)