btrfs: zoned: fix deadlock waiting for ticket during data relocation

When performing data relocation on a zoned filesystem, BTRFS can deadlock
in handle_reserve_tickets(). The relocation process is waiting on a space
reservation ticket that can never be fulfilled, because the relocation
itself is the operation responsible for freeing up that space.

Fix this by introducing a new flush state,
BTRFS_RESERVE_FLUSH_ZONED_RELOCATION, specifically for data chunk
allocation during zoned relocation. Like
BTRFS_RESERVE_FLUSH_FREE_SPACE_INODE, this state uses
priority_reclaim_data_space() instead of the normal flushing path, which
avoids re-entering the relocation code and breaking the deadlock cycle.

In btrfs_alloc_data_chunk_ondemand(), select this new flush state when the
inode belongs to a data relocation root on a zoned filesystem.

Fixes: e2a7fd22378f ("btrfs: zoned: add zone reclaim flush state for DATA space_info")
Reviewed-by: Boris Burkov <boris@bur.io>
Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/delalloc-space.c b/fs/btrfs/delalloc-space.c
index 0970799..4293a63 100644 (file)
--- a/fs/btrfs/delalloc-space.c
+++ b/fs/btrfs/delalloc-space.c
@@ -134,6 +134,8 @@ int btrfs_alloc_data_chunk_ondemand(const struct btrfs_inode *inode, u64 bytes)
 
        if (btrfs_is_free_space_inode(inode))
                flush = BTRFS_RESERVE_FLUSH_FREE_SPACE_INODE;
+       else if (btrfs_is_zoned(fs_info) && btrfs_is_data_reloc_root(root))
+               flush = BTRFS_RESERVE_FLUSH_ZONED_RELOCATION;
 
        return btrfs_reserve_data_bytes(data_sinfo_for_inode(inode), bytes, flush);
 }

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index 7399844..e664159 100644 (file)
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -1705,6 +1705,7 @@ static int handle_reserve_ticket(struct btrfs_space_info *space_info,
                                                ARRAY_SIZE(evict_flush_states));
                break;
        case BTRFS_RESERVE_FLUSH_FREE_SPACE_INODE:
+       case BTRFS_RESERVE_FLUSH_ZONED_RELOCATION:
                priority_reclaim_data_space(space_info, ticket);
                break;
        default:
@@ -1968,6 +1969,7 @@ int btrfs_reserve_data_bytes(struct btrfs_space_info *space_info, u64 bytes,
 
        ASSERT(flush == BTRFS_RESERVE_FLUSH_DATA ||
               flush == BTRFS_RESERVE_FLUSH_FREE_SPACE_INODE ||
+              flush == BTRFS_RESERVE_FLUSH_ZONED_RELOCATION ||
               flush == BTRFS_RESERVE_NO_FLUSH, "flush=%d", flush);
        ASSERT(!current->journal_info || flush != BTRFS_RESERVE_FLUSH_DATA,
               "current->journal_info=0x%lx flush=%d",

diff --git a/fs/btrfs/space-info.h b/fs/btrfs/space-info.h
index 24f4507..aa836e8 100644 (file)
--- a/fs/btrfs/space-info.h
+++ b/fs/btrfs/space-info.h
@@ -77,6 +77,17 @@ enum btrfs_reserve_flush_enum {
         */
        BTRFS_RESERVE_FLUSH_ALL_STEAL,
 
+       /*
+        * This is for relocation on zoned filesystems only. We need to use
+        * priority flushing for this, because otherwise we can deadlock on
+        * waiting for a ticket, that cannot be granted, because we cannot do
+        * any allocations.
+        *
+        * Apart from being specific to zoned relocation, it is equal to
+        * BTRFS_FLUSH_FREE_SPACE_INODE.
+        */
+       BTRFS_RESERVE_FLUSH_ZONED_RELOCATION,
+
        /*
         * This is for btrfs_use_block_rsv only.  We have exhausted our block
         * rsv and our global block rsv.  This can happen for things like