xfs: don't leak xfs_buf_cancel structures when recovery fails

If log recovery fails, we free the memory used by the buffer
cancellation buckets, but we don't actually traverse each bucket list to
free the individual xfs_buf_cancel objects. This leads to a memory
leak, as reported by kmemleak in xfs/051:

unreferenced object 0xffff888103629560 (size 32):
comm "mount", pid 687045, jiffies 4296935916 (age 10.752s)
hex dump (first 32 bytes):
08 d3 0a 01 00 00 00 00 08 00 00 00 01 00 00 00 ................
d0 f5 0b 92 81 88 ff ff 80 64 64 25 81 88 ff ff .........dd%....
backtrace:
[<ffffffffa0317c83>] kmem_alloc+0x73/0x140 [xfs]
[<ffffffffa03234a9>] xlog_recover_buf_commit_pass1+0x139/0x200 [xfs]
[<ffffffffa032dc27>] xlog_recover_commit_trans+0x307/0x350 [xfs]
[<ffffffffa032df15>] xlog_recovery_process_trans+0xa5/0xe0 [xfs]
[<ffffffffa032e12d>] xlog_recover_process_data+0x8d/0x140 [xfs]
[<ffffffffa032e49d>] xlog_do_recovery_pass+0x19d/0x740 [xfs]
[<ffffffffa032f22d>] xlog_do_log_recovery+0x6d/0x150 [xfs]
[<ffffffffa032f343>] xlog_do_recover+0x33/0x1d0 [xfs]
[<ffffffffa032faba>] xlog_recover+0xda/0x190 [xfs]
[<ffffffffa03194bc>] xfs_log_mount+0x14c/0x360 [xfs]
[<ffffffffa030bfed>] xfs_mountfs+0x50d/0xa60 [xfs]
[<ffffffffa03124b5>] xfs_fs_fill_super+0x6a5/0x950 [xfs]
[<ffffffff812b92a5>] get_tree_bdev+0x175/0x280
[<ffffffff812b7c3a>] vfs_get_tree+0x1a/0x80
[<ffffffff812e366f>] path_mount+0x6ff/0xaa0
[<ffffffff812e3b13>] __x64_sys_mount+0x103/0x140

Signed-off-by: Darrick J. Wong <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Dave Chinner <[e-mail]>
Signed-off-by: Dave Chinner <[e-mail]>

fs/xfs/xfs_buf_item_recover.c

···
 xlog_free_buf_cancel_table(
 	struct xlog	*log)
 {
+	int		i;
+
 	if (!log->l_buf_cancel_table)
 		return;
+
+	for (i = 0; i < XLOG_BC_TABLE_SIZE; i++) {
+		struct xfs_buf_cancel	*bc;
+
+		while ((bc = list_first_entry_or_null(
+				&log->l_buf_cancel_table[i],
+				struct xfs_buf_cancel, bc_list))) {
+			list_del(&bc->bc_list);
+			kmem_free(bc);
+		}
+	}
 
 	kmem_free(log->l_buf_cancel_table);
 	log->l_buf_cancel_table = NULL;