[Ocfs2-devel] [PATCH] ocfs2: fix the oops problem when write cloned file

Gang He
2020-01-23T03:17:33Z

Hello Guys,

Happy Lunar New Year.
If you are free, please help to review this patch.
Since this is a regression issue, broke writing cloned files.
The root cause is inode buffer head is NULL when calling ocfs2_refcount_cow.

Thanks
Gang

> -----Original Message-----
> From: Gang He
> Sent: 2020?1?21? 13:02
> To: mark at fasheh.com; jlbec at evilplan.org; joseph.qi at
linux.alibaba.com
> Cc: Gang He <GHe at suse.com>; linux-kernel at vger.kernel.org;
> ocfs2-devel at oss.oracle.com; akpm at linux-foundation.org
> Subject: [PATCH] ocfs2: fix the oops problem when write cloned file
>
> Writing a cloned file triggers a kernel oops and the user-space command
> process is also killed by the system.
> The bug can be reproduced stably, e.g.
> 1)create a file under ocfs2 file system directory.
>   journalctl -b > aa.txt
> 2)create a cloned file for this file.
>   reflink aa.txt bb.txt
> 3)write the cloned file with dd command.
>   dd if=/dev/zero of=bb.txt bs=512 count=1 conv=notrunc
>
> The dd command is killed by the kernel, then you can see the oops message
> via dmesg command.
>
> [  463.875404] BUG: kernel NULL pointer dereference, address:
> 0000000000000028 [  463.875413] #PF: supervisor read access in kernel
> mode [  463.875416] #PF: error_code(0x0000) - not-present page
> [  463.875418] PGD 0 P4D 0 [  463.875425] Oops: 0000 [#1] SMP PTI
> [  463.875431] CPU: 1 PID: 2291 Comm: dd Tainted: G           OE
> 5.3.16-2-default
> [  463.875433] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS Bochs 01/01/2011 [  463.875500] RIP:
> 0010:ocfs2_refcount_cow+0xa4/0x5d0 [ocfs2] [  463.875505] Code: 06 89
> 6c 24 38 89 eb f6 44 24 3c 02 74 be 49 8b 47 28 [  463.875508] RSP:
> 0018:ffffa2cb409dfce8 EFLAGS: 00010202 [  463.875512] RAX:
> ffff8b1ebdca8000 RBX: 0000000000000001 RCX: ffff8b1eb73a9df0
> [  463.875515] RDX: 0000000000056a01 RSI: 0000000000000000 RDI:
> 0000000000000000 [  463.875517] RBP: 0000000000000001 R08:
> ffff8b1eb73a9de0 R09: 0000000000000000 [  463.875520] R10:
> 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
> [  463.875522] R13: ffff8b1eb922f048 R14: 0000000000000000 R15:
> ffff8b1eb922f048 [  463.875526] FS:  00007f8f44d15540(0000)
> GS:ffff8b1ebeb00000(0000) knlGS:0000000000000000 [  463.875529] CS:
> 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [  463.875532] CR2:
> 0000000000000028 CR3: 000000003c17a000 CR4: 00000000000006e0
> [  463.875546] Call Trace:
> [  463.875596]  ? ocfs2_inode_lock_full_nested+0x18b/0x960 [ocfs2]
> [  463.875648]  ocfs2_file_write_iter+0xaf8/0xc70 [ocfs2] [  463.875672]
> new_sync_write+0x12d/0x1d0 [  463.875688]  vfs_write+0xad/0x1a0
> [  463.875697]  ksys_write+0xa1/0xe0 [  463.875710]
> do_syscall_64+0x60/0x1f0 [  463.875743]
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [  463.875758] RIP: 0033:0x7f8f4482ed44
> [  463.875762] Code: 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 80
00
> 00 00 [  463.875765] RSP: 002b:00007fff300a79d8 EFLAGS: 00000246
> ORIG_RAX: 0000000000000001 [  463.875769] RAX: ffffffffffffffda RBX:
> 0000000000000000 RCX: 00007f8f4482ed44 [  463.875771] RDX:
> 0000000000000200 RSI: 000055f771b5c000 RDI: 0000000000000001
> [  463.875774] RBP: 0000000000000200 R08: 00007f8f44af9c78 R09:
> 0000000000000003 [  463.875776] R10: 000000000000089f R11:
> 0000000000000246 R12: 000055f771b5c000 [  463.875779] R13:
> 0000000000000200 R14: 0000000000000000 R15: 000055f771b5c000
>
> This regression problem was introduced by commit e74540b28556 ("ocfs2:
> protect extent tree in ocfs2_prepare_inode_for_write()").
>
> Fixes: e74540b28556 ("ocfs2: protect extent tree in
> ocfs2_prepare_inode_for_write()").
> Signed-off-by: Gang He <ghe at suse.com>
> ---
>  fs/ocfs2/file.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c index
> 9876db52913a..6cd5e4924e4d 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -2101,17 +2101,15 @@ static int ocfs2_is_io_unaligned(struct inode
> *inode, size_t count, loff_t pos)  static int
> ocfs2_inode_lock_for_extent_tree(struct inode *inode,
>  					    struct buffer_head **di_bh,
>  					    int meta_level,
> -					    int overwrite_io,
>  					    int write_sem,
>  					    int wait)
>  {
>  	int ret = 0;
>
>  	if (wait)
> -		ret = ocfs2_inode_lock(inode, NULL, meta_level);
> +		ret = ocfs2_inode_lock(inode, di_bh, meta_level);
>  	else
> -		ret = ocfs2_try_inode_lock(inode,
> -			overwrite_io ? NULL : di_bh, meta_level);
> +		ret = ocfs2_try_inode_lock(inode, di_bh, meta_level);
>  	if (ret < 0)
>  		goto out;
>
> @@ -2136,6 +2134,7 @@ static int ocfs2_inode_lock_for_extent_tree(struct
> inode *inode,
>
>  out_unlock:
>  	brelse(*di_bh);
> +	*di_bh = NULL;
>  	ocfs2_inode_unlock(inode, meta_level);
>  out:
>  	return ret;
> @@ -2177,7 +2176,6 @@ static int ocfs2_prepare_inode_for_write(struct file
> *file,
>  		ret = ocfs2_inode_lock_for_extent_tree(inode,
>  						       &di_bh,
>  						       meta_level,
> -						       overwrite_io,
>  						       write_sem,
>  						       wait);
>  		if (ret < 0) {
> @@ -2233,13 +2231,13 @@ static int ocfs2_prepare_inode_for_write(struct
> file *file,
>  							   &di_bh,
>  							   meta_level,
>  							   write_sem);
> +			meta_level = 1;
> +			write_sem = 1;
>  			ret = ocfs2_inode_lock_for_extent_tree(inode,
>  							       &di_bh,
>  							       meta_level,
> -							       overwrite_io,
> -							       1,
> +							       write_sem,
>  							       wait);
> -			write_sem = 1;
>  			if (ret < 0) {
>  				if (ret != -EAGAIN)
>  					mlog_errno(ret);
> --
> 2.12.3