[PATCH AUTOSEL 4.19 15/47] btrfs: fix minimum number of chunk errors for DUP

[PATCH AUTOSEL 4.19 15/47] btrfs: fix minimum number of chunk errors for DUP

[Sasha Levin]

From: David Sterba <dsterba@suse.com>

[ Upstream commit 0ee5f8ae082e1f675a2fb6db601c31ac9958a134 ]

The list of profiles in btrfs_chunk_max_errors lists DUP as a profile
DUP able to tolerate 1 device missing. Though this profile is special
with 2 copies, it still needs the device, unlike the others.

Looking at the history of changes, thre's no clear reason why DUP is
there, functions were refactored and blocks of code merged to one
helper.

d20983b40e828 Btrfs: fix writing data into the seed filesystem
  - factor code to a helper

de11cc12df173 Btrfs: don't pre-allocate btrfs bio
  - unrelated change, DUP still in the list with max errors 1

a236aed14ccb0 Btrfs: Deal with failed writes in mirrored configurations
  - introduced the max errors, leaves DUP and RAID1 in the same group

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/btrfs/volumes.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2fd000308be7..6e008bd5c8cd 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5040,8 +5040,7 @@ static inline int btrfs_chunk_max_errors(struct map_lookup *map)
 
 	if (map->type & (BTRFS_BLOCK_GROUP_RAID1 |
 			 BTRFS_BLOCK_GROUP_RAID10 |
-			 BTRFS_BLOCK_GROUP_RAID5 |
-			 BTRFS_BLOCK_GROUP_DUP)) {
+			 BTRFS_BLOCK_GROUP_RAID5)) {
 		max_errors = 1;
 	} else if (map->type & BTRFS_BLOCK_GROUP_RAID6) {
 		max_errors = 2;
-- 
2.20.1

[PATCH AUTOSEL 4.19 16/47] btrfs: qgroup: Don't hold qgroup_ioctl_lock in btrfs_qgroup_inherit()

[Sasha Levin]

From: Qu Wenruo <wqu@suse.com>

[ Upstream commit e88439debd0a7f969b3ddba6f147152cd0732676 ]

[BUG]
Lockdep will report the following circular locking dependency:

  WARNING: possible circular locking dependency detected
  5.2.0-rc2-custom #24 Tainted: G           O
  ------------------------------------------------------
  btrfs/8631 is trying to acquire lock:
  000000002536438c (&fs_info->qgroup_ioctl_lock#2){+.+.}, at: btrfs_qgroup_inherit+0x40/0x620 [btrfs]

  but task is already holding lock:
  000000003d52cc23 (&fs_info->tree_log_mutex){+.+.}, at: create_pending_snapshot+0x8b6/0xe60 [btrfs]

  which lock already depends on the new lock.

  the existing dependency chain (in reverse order) is:

  -> #2 (&fs_info->tree_log_mutex){+.+.}:
         __mutex_lock+0x76/0x940
         mutex_lock_nested+0x1b/0x20
         btrfs_commit_transaction+0x475/0xa00 [btrfs]
         btrfs_commit_super+0x71/0x80 [btrfs]
         close_ctree+0x2bd/0x320 [btrfs]
         btrfs_put_super+0x15/0x20 [btrfs]
         generic_shutdown_super+0x72/0x110
         kill_anon_super+0x18/0x30
         btrfs_kill_super+0x16/0xa0 [btrfs]
         deactivate_locked_super+0x3a/0x80
         deactivate_super+0x51/0x60
         cleanup_mnt+0x3f/0x80
         __cleanup_mnt+0x12/0x20
         task_work_run+0x94/0xb0
         exit_to_usermode_loop+0xd8/0xe0
         do_syscall_64+0x210/0x240
         entry_SYSCALL_64_after_hwframe+0x49/0xbe

  -> #1 (&fs_info->reloc_mutex){+.+.}:
         __mutex_lock+0x76/0x940
         mutex_lock_nested+0x1b/0x20
         btrfs_commit_transaction+0x40d/0xa00 [btrfs]
         btrfs_quota_enable+0x2da/0x730 [btrfs]
         btrfs_ioctl+0x2691/0x2b40 [btrfs]
         do_vfs_ioctl+0xa9/0x6d0
         ksys_ioctl+0x67/0x90
         __x64_sys_ioctl+0x1a/0x20
         do_syscall_64+0x65/0x240
         entry_SYSCALL_64_after_hwframe+0x49/0xbe

  -> #0 (&fs_info->qgroup_ioctl_lock#2){+.+.}:
         lock_acquire+0xa7/0x190
         __mutex_lock+0x76/0x940
         mutex_lock_nested+0x1b/0x20
         btrfs_qgroup_inherit+0x40/0x620 [btrfs]
         create_pending_snapshot+0x9d7/0xe60 [btrfs]
         create_pending_snapshots+0x94/0xb0 [btrfs]
         btrfs_commit_transaction+0x415/0xa00 [btrfs]
         btrfs_mksubvol+0x496/0x4e0 [btrfs]
         btrfs_ioctl_snap_create_transid+0x174/0x180 [btrfs]
         btrfs_ioctl_snap_create_v2+0x11c/0x180 [btrfs]
         btrfs_ioctl+0xa90/0x2b40 [btrfs]
         do_vfs_ioctl+0xa9/0x6d0
         ksys_ioctl+0x67/0x90
         __x64_sys_ioctl+0x1a/0x20
         do_syscall_64+0x65/0x240
         entry_SYSCALL_64_after_hwframe+0x49/0xbe

  other info that might help us debug this:

  Chain exists of:
    &fs_info->qgroup_ioctl_lock#2 --> &fs_info->reloc_mutex --> &fs_info->tree_log_mutex

   Possible unsafe locking scenario:

         CPU0                    CPU1
         ----                    ----
    lock(&fs_info->tree_log_mutex);
                                 lock(&fs_info->reloc_mutex);
                                 lock(&fs_info->tree_log_mutex);
    lock(&fs_info->qgroup_ioctl_lock#2);

   *** DEADLOCK ***

  6 locks held by btrfs/8631:
   #0: 00000000ed8f23f6 (sb_writers#12){.+.+}, at: mnt_want_write_file+0x28/0x60
   #1: 000000009fb1597a (&type->i_mutex_dir_key#10/1){+.+.}, at: btrfs_mksubvol+0x70/0x4e0 [btrfs]
   #2: 0000000088c5ad88 (&fs_info->subvol_sem){++++}, at: btrfs_mksubvol+0x128/0x4e0 [btrfs]
   #3: 000000009606fc3e (sb_internal#2){.+.+}, at: start_transaction+0x37a/0x520 [btrfs]
   #4: 00000000f82bbdf5 (&fs_info->reloc_mutex){+.+.}, at: btrfs_commit_transaction+0x40d/0xa00 [btrfs]
   #5: 000000003d52cc23 (&fs_info->tree_log_mutex){+.+.}, at: create_pending_snapshot+0x8b6/0xe60 [btrfs]

[CAUSE]
Due to the delayed subvolume creation, we need to call
btrfs_qgroup_inherit() inside commit transaction code, with a lot of
other mutex hold.
This hell of lock chain can lead to above problem.

[FIX]
On the other hand, we don't really need to hold qgroup_ioctl_lock if
we're in the context of create_pending_snapshot().
As in that context, we're the only one being able to modify qgroup.

All other qgroup functions which needs qgroup_ioctl_lock are either
holding a transaction handle, or will start a new transaction:
  Functions will start a new transaction():
  * btrfs_quota_enable()
  * btrfs_quota_disable()
  Functions hold a transaction handler:
  * btrfs_add_qgroup_relation()
  * btrfs_del_qgroup_relation()
  * btrfs_create_qgroup()
  * btrfs_remove_qgroup()
  * btrfs_limit_qgroup()
  * btrfs_qgroup_inherit() call inside create_subvol()

So we have a higher level protection provided by transaction, thus we
don't need to always hold qgroup_ioctl_lock in btrfs_qgroup_inherit().

Only the btrfs_qgroup_inherit() call in create_subvol() needs to hold
qgroup_ioctl_lock, while the btrfs_qgroup_inherit() call in
create_pending_snapshot() is already protected by transaction.

So the fix is to detect the context by checking
trans->transaction->state.
If we're at TRANS_STATE_COMMIT_DOING, then we're in commit transaction
context and no need to get the mutex.

Reported-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/btrfs/qgroup.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index e46e83e87600..734866ab5194 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2249,6 +2249,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
 	int ret = 0;
 	int i;
 	u64 *i_qgroups;
+	bool committing = false;
 	struct btrfs_fs_info *fs_info = trans->fs_info;
 	struct btrfs_root *quota_root;
 	struct btrfs_qgroup *srcgroup;
@@ -2256,7 +2257,25 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
 	u32 level_size = 0;
 	u64 nums;
 
-	mutex_lock(&fs_info->qgroup_ioctl_lock);
+	/*
+	 * There are only two callers of this function.
+	 *
+	 * One in create_subvol() in the ioctl context, which needs to hold
+	 * the qgroup_ioctl_lock.
+	 *
+	 * The other one in create_pending_snapshot() where no other qgroup
+	 * code can modify the fs as they all need to either start a new trans
+	 * or hold a trans handler, thus we don't need to hold
+	 * qgroup_ioctl_lock.
+	 * This would avoid long and complex lock chain and make lockdep happy.
+	 */
+	spin_lock(&fs_info->trans_lock);
+	if (trans->transaction->state == TRANS_STATE_COMMIT_DOING)
+		committing = true;
+	spin_unlock(&fs_info->trans_lock);
+
+	if (!committing)
+		mutex_lock(&fs_info->qgroup_ioctl_lock);
 	if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags))
 		goto out;
 
@@ -2420,7 +2439,8 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
 unlock:
 	spin_unlock(&fs_info->qgroup_lock);
 out:
-	mutex_unlock(&fs_info->qgroup_ioctl_lock);
+	if (!committing)
+		mutex_unlock(&fs_info->qgroup_ioctl_lock);
 	return ret;
 }
 
-- 
2.20.1