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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
CC:     Liu Bo <bo.li.liu@oracle.com>, David Sterba <dsterba@suse.com>,
        "Sasha Levin" <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.14 049/100] Btrfs: fix list_add corruption and
 soft lockups in fsync
Thread-Topic: [PATCH AUTOSEL for 4.14 049/100] Btrfs: fix list_add corruption
 and soft lockups in fsync
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Date:   Wed, 24 Jan 2018 04:14:49 +0000
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From: Liu Bo <bo.li.liu@oracle.com>

[ Upstream commit ebb70442cdd4872260c2415929c456be3562da82 ]

Xfstests btrfs/146 revealed this corruption,

[   58.138831] Buffer I/O error on dev dm-0, logical block 2621424, async p=
age read
[   58.151233] BTRFS error (device sdf): bdev /dev/mapper/error-test errs: =
wr 1, rd 0, flush 0, corrupt 0, gen 0
[   58.152403] list_add corruption. prev->next should be next (ffff88005e67=
75d8), but was ffffc9000189be88. (prev=3Dffffc9000189be88).
[   58.153518] ------------[ cut here ]------------
[   58.153892] WARNING: CPU: 1 PID: 1287 at lib/list_debug.c:31 __list_add_=
valid+0x169/0x1f0
...
[   58.157379] RIP: 0010:__list_add_valid+0x169/0x1f0
...
[   58.161956] Call Trace:
[   58.162264]  btrfs_log_inode_parent+0x5bd/0xfb0 [btrfs]
[   58.163583]  btrfs_log_dentry_safe+0x60/0x80 [btrfs]
[   58.164003]  btrfs_sync_file+0x4c2/0x6f0 [btrfs]
[   58.164393]  vfs_fsync_range+0x5f/0xd0
[   58.164898]  do_fsync+0x5a/0x90
[   58.165170]  SyS_fsync+0x10/0x20
[   58.165395]  entry_SYSCALL_64_fastpath+0x1f/0xbe
...

It turns out that we could record btrfs_log_ctx:io_err in
log_one_extents when IO fails, but make log_one_extents() return '0'
instead of -EIO, so the IO error is not acknowledged by the callers,
i.e.  btrfs_log_inode_parent(), which would remove btrfs_log_ctx:list
from list head 'root->log_ctxs'.  Since btrfs_log_ctx is allocated
from stack memory, it'd get freed with a object alive on the
list. then a future list_add will throw the above warning.

This returns the correct error in the above case.

Jeff also reported this while testing against his fsync error
patch set[1].

[1]: https://www.spinics.net/lists/linux-btrfs/msg65308.html
"btrfs list corruption and soft lockups while testing writeback error handl=
ing"

Fixes: 8407f553268a4611f254 ("Btrfs: fix data corruption after fast fsync a=
nd writeback error")
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 fs/btrfs/file.c     | 5 +++--
 fs/btrfs/tree-log.c | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index aafcc785f840..d564a7049d7f 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2056,6 +2056,8 @@ int btrfs_sync_file(struct file *file, loff_t start, =
loff_t end, int datasync)
 	len =3D (u64)end - (u64)start + 1;
 	trace_btrfs_sync_file(file, datasync);
=20
+	btrfs_init_log_ctx(&ctx, inode);
+
 	/*
 	 * We write the dirty pages in the range and wait until they complete
 	 * out of the ->i_mutex. If so, we can flush the dirty pages by
@@ -2202,8 +2204,6 @@ int btrfs_sync_file(struct file *file, loff_t start, =
loff_t end, int datasync)
 	}
 	trans->sync =3D true;
=20
-	btrfs_init_log_ctx(&ctx, inode);
-
 	ret =3D btrfs_log_dentry_safe(trans, root, dentry, start, end, &ctx);
 	if (ret < 0) {
 		/* Fallthrough and commit/free transaction. */
@@ -2261,6 +2261,7 @@ int btrfs_sync_file(struct file *file, loff_t start, =
loff_t end, int datasync)
 		ret =3D btrfs_end_transaction(trans);
 	}
 out:
+	ASSERT(list_empty(&ctx.list));
 	err =3D file_check_and_advance_wb_err(file);
 	if (!ret)
 		ret =3D err;
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index c800d067fcbf..d3002842d7f6 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -4100,7 +4100,7 @@ static int log_one_extent(struct btrfs_trans_handle *=
trans,
=20
 	if (ordered_io_err) {
 		ctx->io_err =3D -EIO;
-		return 0;
+		return ctx->io_err;
 	}
=20
 	btrfs_init_map_token(&token);
--=20
2.11.0