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Message-ID: <20260130025339.51519-1-me@linux.beauty>
Date: Fri, 30 Jan 2026 10:53:38 +0800
From: Li Chen <me@...ux.beauty>
To: "Theodore Ts'o" <tytso@....edu>,
Andreas Dilger <adilger.kernel@...ger.ca>,
Jan Kara <jack@...e.cz>,
linux-ext4@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org,
Li Chen <me@...ux.beauty>
Subject: [PATCH v2] ext4: publish jinode after initialization
ext4_inode_attach_jinode() publishes ei->jinode to concurrent users.
It used to set ei->jinode before jbd2_journal_init_jbd_inode(),
allowing a reader to observe a non-NULL jinode with i_vfs_inode
still unset.
The fast commit flush path can then pass this jinode to
jbd2_wait_inode_data(), which dereferences i_vfs_inode->i_mapping and
may crash.
Below is the crash I observe:
```
BUG: unable to handle page fault for address: 000000010beb47f4
PGD 110e51067 P4D 110e51067 PUD 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 1 UID: 0 PID: 4850 Comm: fc_fsync_bench_ Not tainted 6.18.0-00764-g795a690c06a5 #1 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.17.0-2-2 04/01/2014
RIP: 0010:xas_find_marked+0x3d/0x2e0
Code: e0 03 48 83 f8 02 0f 84 f0 01 00 00 48 8b 47 08 48 89 c3 48 39 c6 0f 82 fd 01 00 00 48 85 c9 74 3d 48 83 f9 03 77 63 4c 8b 0f <49> 8b 71 08 48 c7 47 18 00 00 00 00 48 89 f1 83 e1 03 48 83 f9 02
RSP: 0018:ffffbbee806e7bf0 EFLAGS: 00010246
RAX: 000000000010beb4 RBX: 000000000010beb4 RCX: 0000000000000003
RDX: 0000000000000001 RSI: 0000002000300000 RDI: ffffbbee806e7c10
RBP: 0000000000000001 R08: 0000002000300000 R09: 000000010beb47ec
R10: ffff9ea494590090 R11: 0000000000000000 R12: 0000002000300000
R13: ffffbbee806e7c90 R14: ffff9ea494513788 R15: ffffbbee806e7c88
FS: 00007fc2f9e3e6c0(0000) GS:ffff9ea6b1444000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000010beb47f4 CR3: 0000000119ac5000 CR4: 0000000000750ef0
PKRU: 55555554
Call Trace:
<TASK>
filemap_get_folios_tag+0x87/0x2a0
__filemap_fdatawait_range+0x5f/0xd0
? srso_alias_return_thunk+0x5/0xfbef5
? __schedule+0x3e7/0x10c0
? srso_alias_return_thunk+0x5/0xfbef5
? srso_alias_return_thunk+0x5/0xfbef5
? srso_alias_return_thunk+0x5/0xfbef5
? preempt_count_sub+0x5f/0x80
? srso_alias_return_thunk+0x5/0xfbef5
? cap_safe_nice+0x37/0x70
? srso_alias_return_thunk+0x5/0xfbef5
? preempt_count_sub+0x5f/0x80
? srso_alias_return_thunk+0x5/0xfbef5
filemap_fdatawait_range_keep_errors+0x12/0x40
ext4_fc_commit+0x697/0x8b0
? ext4_file_write_iter+0x64b/0x950
? srso_alias_return_thunk+0x5/0xfbef5
? preempt_count_sub+0x5f/0x80
? srso_alias_return_thunk+0x5/0xfbef5
? vfs_write+0x356/0x480
? srso_alias_return_thunk+0x5/0xfbef5
? preempt_count_sub+0x5f/0x80
ext4_sync_file+0xf7/0x370
do_fsync+0x3b/0x80
? syscall_trace_enter+0x108/0x1d0
__x64_sys_fdatasync+0x16/0x20
do_syscall_64+0x62/0x2c0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
...
```
Fix this by initializing the jbd2_inode first.
Use smp_wmb() and WRITE_ONCE() to publish ei->jinode after
initialization. Readers use READ_ONCE() to fetch the pointer.
Fixes: a361293f5fede ("jbd2: Fix oops in jbd2_journal_file_inode()")
Cc: stable@...r.kernel.org
Signed-off-by: Li Chen <me@...ux.beauty>
---
Changes since v1:
- Publish EXT4_I(inode)->jinode with smp_wmb() + WRITE_ONCE(), and fetch it
with READ_ONCE() (instead of smp_store_release()/smp_load_acquire()), as
suggeted by Jan.
fs/ext4/ext4_jbd2.h | 16 ++++++++++++----
fs/ext4/fast_commit.c | 7 +++++--
fs/ext4/inode.c | 15 +++++++++++----
fs/ext4/super.c | 11 +++++++----
4 files changed, 35 insertions(+), 14 deletions(-)
diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
index 63d17c5201b5..2d5343441b71 100644
--- a/fs/ext4/ext4_jbd2.h
+++ b/fs/ext4/ext4_jbd2.h
@@ -336,18 +336,26 @@ static inline int ext4_journal_force_commit(journal_t *journal)
static inline int ext4_jbd2_inode_add_write(handle_t *handle,
struct inode *inode, loff_t start_byte, loff_t length)
{
- if (ext4_handle_valid(handle))
+ if (ext4_handle_valid(handle)) {
+ struct jbd2_inode *jinode;
+
+ jinode = READ_ONCE(EXT4_I(inode)->jinode);
return jbd2_journal_inode_ranged_write(handle,
- EXT4_I(inode)->jinode, start_byte, length);
+ jinode, start_byte, length);
+ }
return 0;
}
static inline int ext4_jbd2_inode_add_wait(handle_t *handle,
struct inode *inode, loff_t start_byte, loff_t length)
{
- if (ext4_handle_valid(handle))
+ if (ext4_handle_valid(handle)) {
+ struct jbd2_inode *jinode;
+
+ jinode = READ_ONCE(EXT4_I(inode)->jinode);
return jbd2_journal_inode_ranged_wait(handle,
- EXT4_I(inode)->jinode, start_byte, length);
+ jinode, start_byte, length);
+ }
return 0;
}
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index f575751f1cae..a80ed2d6df81 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -972,16 +972,19 @@ static int ext4_fc_flush_data(journal_t *journal)
struct super_block *sb = journal->j_private;
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct ext4_inode_info *ei;
+ struct jbd2_inode *jinode;
int ret = 0;
list_for_each_entry(ei, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
- ret = jbd2_submit_inode_data(journal, ei->jinode);
+ jinode = READ_ONCE(ei->jinode);
+ ret = jbd2_submit_inode_data(journal, jinode);
if (ret)
return ret;
}
list_for_each_entry(ei, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
- ret = jbd2_wait_inode_data(journal, ei->jinode);
+ jinode = READ_ONCE(ei->jinode);
+ ret = jbd2_wait_inode_data(journal, jinode);
if (ret)
return ret;
}
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index da96db5f2345..d99296d7315f 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -128,6 +128,8 @@ void ext4_inode_csum_set(struct inode *inode, struct ext4_inode *raw,
static inline int ext4_begin_ordered_truncate(struct inode *inode,
loff_t new_size)
{
+ struct jbd2_inode *jinode = READ_ONCE(EXT4_I(inode)->jinode);
+
trace_ext4_begin_ordered_truncate(inode, new_size);
/*
* If jinode is zero, then we never opened the file for
@@ -135,10 +137,10 @@ static inline int ext4_begin_ordered_truncate(struct inode *inode,
* jbd2_journal_begin_ordered_truncate() since there's no
* outstanding writes we need to flush.
*/
- if (!EXT4_I(inode)->jinode)
+ if (!jinode)
return 0;
return jbd2_journal_begin_ordered_truncate(EXT4_JOURNAL(inode),
- EXT4_I(inode)->jinode,
+ jinode,
new_size);
}
@@ -4478,8 +4480,13 @@ int ext4_inode_attach_jinode(struct inode *inode)
spin_unlock(&inode->i_lock);
return -ENOMEM;
}
- ei->jinode = jinode;
- jbd2_journal_init_jbd_inode(ei->jinode, inode);
+ jbd2_journal_init_jbd_inode(jinode, inode);
+ /*
+ * Publish ->jinode only after it is fully initialized so that
+ * readers never observe a partially initialized jbd2_inode.
+ */
+ smp_wmb();
+ WRITE_ONCE(ei->jinode, jinode);
jinode = NULL;
}
spin_unlock(&inode->i_lock);
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 69eb63dde983..5cf6c2b54bbb 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1526,17 +1526,20 @@ static void destroy_inodecache(void)
void ext4_clear_inode(struct inode *inode)
{
+ struct jbd2_inode *jinode;
+
ext4_fc_del(inode);
invalidate_inode_buffers(inode);
clear_inode(inode);
ext4_discard_preallocations(inode);
ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
dquot_drop(inode);
- if (EXT4_I(inode)->jinode) {
+ jinode = READ_ONCE(EXT4_I(inode)->jinode);
+ if (jinode) {
jbd2_journal_release_jbd_inode(EXT4_JOURNAL(inode),
- EXT4_I(inode)->jinode);
- jbd2_free_inode(EXT4_I(inode)->jinode);
- EXT4_I(inode)->jinode = NULL;
+ jinode);
+ jbd2_free_inode(jinode);
+ WRITE_ONCE(EXT4_I(inode)->jinode, NULL);
}
fscrypt_put_encryption_info(inode);
fsverity_cleanup_inode(inode);
--
2.52.0
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