linux-kernel - [PATCH] xfs: fix BUG_ON in xfs

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Date:   Mon, 27 Mar 2023 22:02:18 +0800
From:   Ye Bin <yebin@...weicloud.com>
To:     djwong@...nel.org, linux-xfs@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Ye Bin <yebin10@...wei.com>
Subject: [PATCH] xfs: fix BUG_ON in xfs_getbmap()

From: Ye Bin <yebin10@...wei.com>

There's issue as follows:
XFS: Assertion failed: (bmv->bmv_iflags & BMV_IF_DELALLOC) != 0, file: fs/xfs/xfs_bmap_util.c, line: 329
------------[ cut here ]------------
kernel BUG at fs/xfs/xfs_message.c:102!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 14612 Comm: xfs_io Not tainted 6.3.0-rc2-next-20230315-00006-g2729d23ddb3b-dirty #422
RIP: 0010:assfail+0x96/0xa0
RSP: 0018:ffffc9000fa178c0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffff888179a18000
RDX: 0000000000000000 RSI: ffff888179a18000 RDI: 0000000000000002
RBP: 0000000000000000 R08: ffffffff8321aab6 R09: 0000000000000000
R10: 0000000000000001 R11: ffffed1105f85139 R12: ffffffff8aacc4c0
R13: 0000000000000149 R14: ffff888269f58000 R15: 000000000000000c
FS:  00007f42f27a4740(0000) GS:ffff88882fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000b92388 CR3: 000000024f006000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 xfs_getbmap+0x1a5b/0x1e40
 xfs_ioc_getbmap+0x1fd/0x5b0
 xfs_file_ioctl+0x2cb/0x1d50
 __x64_sys_ioctl+0x197/0x210
 do_syscall_64+0x39/0xb0
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Above issue may happen as follows:
         ThreadA                       ThreadB
do_shared_fault
 __do_fault
  xfs_filemap_fault
   __xfs_filemap_fault
    filemap_fault
                             xfs_ioc_getbmap -> Without BMV_IF_DELALLOC flag
			      xfs_getbmap
			       xfs_ilock(ip, XFS_IOLOCK_SHARED);
			       filemap_write_and_wait
 do_page_mkwrite
  xfs_filemap_page_mkwrite
   __xfs_filemap_fault
    xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
    iomap_page_mkwrite
     ...
     xfs_buffered_write_iomap_begin
      xfs_bmapi_reserve_delalloc -> Allocate delay extent
                              xfs_ilock_data_map_shared(ip)
	                      xfs_getbmap_report_one
			       ASSERT((bmv->bmv_iflags & BMV_IF_DELALLOC) != 0)
	                        -> trigger BUG_ON

As xfs_filemap_page_mkwrite() only hold XFS_MMAPLOCK_SHARED lock, there's
small window mkwrite can produce delay extent after file write in xfs_getbmap().
To solve above issue, hold XFS_MMAPLOCK_EXCL lock when do xfs_getbmap(),
to prevent write operations by do_page_mkwrite().
During doing __xfs_filemap_fault() we can't hold IOLOCK lock, as it's may lead
to ABBA dealock with xfs_file_write_iter().It's very easy to reproduce when
do fsstress, lockdep will detect deadlock.

Signed-off-by: Ye Bin <yebin10@...wei.com>
---
 fs/xfs/xfs_bmap_util.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index a09dd2606479..f23771a0cc8d 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -463,11 +463,13 @@ xfs_getbmap(
 			max_len = XFS_ISIZE(ip);
 		break;
 	case XFS_DATA_FORK:
+		lock = XFS_MMAPLOCK_EXCL;
+		xfs_ilock(ip, lock);
 		if (!(iflags & BMV_IF_DELALLOC) &&
 		    (ip->i_delayed_blks || XFS_ISIZE(ip) > ip->i_disk_size)) {
 			error = filemap_write_and_wait(VFS_I(ip)->i_mapping);
 			if (error)
-				goto out_unlock_iolock;
+				goto out_unlock_ilock;
 
 			/*
 			 * Even after flushing the inode, there can still be
@@ -486,7 +488,7 @@ xfs_getbmap(
 		else
 			max_len = XFS_ISIZE(ip);
 
-		lock = xfs_ilock_data_map_shared(ip);
+		lock |= xfs_ilock_data_map_shared(ip);
 		break;
 	}
 
-- 
2.31.1