Re: [PATCH] xfs: Fix the free logic of state in xfs_attr_node_hasname

xuyang2018.jy
2021-11-01T06:33:30Z

On 2021/10/30 2:50, Darrick J. Wong wrote:
> [adding the resident xattrs expert]
>
> On Fri, Oct 29, 2021 at 04:52:00PM +0800, Yang Xu wrote:
>> When testing xfstests xfs/126 on lastest upstream kernel, it will hang on some machine.
>> Adding a getxattr operation after xattr corrupted, I can reproduce it 100%.
>>
>> The deadlock as below:
>> [983.923403] task:setfattr state:D stack: 0 pid:17639 ppid: 14687 flags:0x00000080
>> [ 983.923405] Call Trace:
>> [ 983.923410] __schedule+0x2c4/0x700
>> [ 983.923412] schedule+0x37/0xa0
>> [ 983.923414] schedule_timeout+0x274/0x300
>> [ 983.923416] __down+0x9b/0xf0
>> [ 983.923451] ? xfs_buf_find.isra.29+0x3c8/0x5f0 [xfs]
>> [ 983.923453] down+0x3b/0x50
>> [ 983.923471] xfs_buf_lock+0x33/0xf0 [xfs]
>> [ 983.923490] xfs_buf_find.isra.29+0x3c8/0x5f0 [xfs]
>> [ 983.923508] xfs_buf_get_map+0x4c/0x320 [xfs]
>> [ 983.923525] xfs_buf_read_map+0x53/0x310 [xfs]
>> [ 983.923541] ? xfs_da_read_buf+0xcf/0x120 [xfs]
>> [ 983.923560] xfs_trans_read_buf_map+0x1cf/0x360 [xfs]
>> [ 983.923575] ? xfs_da_read_buf+0xcf/0x120 [xfs]
>> [ 983.923590] xfs_da_read_buf+0xcf/0x120 [xfs]
>> [ 983.923606] xfs_da3_node_read+0x1f/0x40 [xfs]
>> [ 983.923621] xfs_da3_node_lookup_int+0x69/0x4a0 [xfs]
>> [ 983.923624] ? kmem_cache_alloc+0x12e/0x270
>> [ 983.923637] xfs_attr_node_hasname+0x6e/0xa0 [xfs]
>> [ 983.923651] xfs_has_attr+0x6e/0xd0 [xfs]
>> [ 983.923664] xfs_attr_set+0x273/0x320 [xfs]
>> [ 983.923683] xfs_xattr_set+0x87/0xd0 [xfs]
>> [ 983.923686] __vfs_removexattr+0x4d/0x60
>> [ 983.923688] __vfs_removexattr_locked+0xac/0x130
>> [ 983.923689] vfs_removexattr+0x4e/0xf0
>> [ 983.923690] removexattr+0x4d/0x80
>> [ 983.923693] ? __check_object_size+0xa8/0x16b
>> [ 983.923695] ? strncpy_from_user+0x47/0x1a0
>> [ 983.923696] ? getname_flags+0x6a/0x1e0
>> [ 983.923697] ? _cond_resched+0x15/0x30
>> [ 983.923699] ? __sb_start_write+0x1e/0x70
>> [ 983.923700] ? mnt_want_write+0x28/0x50
>> [ 983.923701] path_removexattr+0x9b/0xb0
>> [ 983.923702] __x64_sys_removexattr+0x17/0x20
>> [ 983.923704] do_syscall_64+0x5b/0x1a0
>> [ 983.923705] entry_SYSCALL_64_after_hwframe+0x65/0xca
>> [ 983.923707] RIP: 0033:0x7f080f10ee1b
>>
>> When getxattr calls xfs_attr_node_get, xfs_da3_node_lookup_int fails in
>> xfs_attr_node_hasname because we have use blocktrash to random it in xfs/126. So it
>> free stat and xfs_attr_node_get doesn't do xfs_buf_trans release job.
>>
>> Then subsequent removexattr will hang because of it.
>>
>> This bug was introduced by kernel commit 07120f1abdff ("xfs: Add xfs_has_attr and subroutines").
>> It adds xfs_attr_node_hasname helper and said caller will be responsible for freeing the state
>> in this case. But xfs_attr_node_hasname will free stat itself instead of caller if
>> xfs_da3_node_lookup_int fails.
>>
>> Fix this bug by moving the step of free state into caller.
>>
>> Fixes: 07120f1abdff ("xfs: Add xfs_has_attr and subroutines")
>> Signed-off-by: Yang Xu<xuyang2018.jy@fujitsu.com>
>
> Ah, I knew this function was gross. Before, we would set *statep to
> NULL upon entry to the function, and we would pass the newly allocated
> da state back out if !error. However, the caller has no idea if the
> return value came from error or retval, other than (I guess) the comment
> implies (or had better imply) that ENOATTR/EEXIST only come from retval.
>
> Now you're changing it to always pass state out via **statep even if the
> da3 lookup returns error and we want to pass that out. But then
> xfs_attr_node_addname_find_attr does this:
>
> retval = xfs_attr_node_hasname(args,&dac->da_state);
> if (retval != -ENOATTR&& retval != -EEXIST)
> return error;
>
> without ever clearing dac->da_state. Won't that leak the da state?
Yes. We should clear dac->da_state here by using goto error instead of
return error.
>
> Granted, I wonder if the xfs_attr_node_hasname call in
> xfs_attr_node_removename_setup will also leak the state if the return
> value is ENOATTR?
Yes, it will also leak the state if error is not EEXIST. Will fix them
in v2.
>
> If you ask me the whole ENOATTR/EEXIST thing still needs to be replaced
> with an enum xfs_attr_lookup_result passed out separately so that we
> don't have to think about which magic errno values are not really
> errors.
Agree.

Best Regards
Yang Xu
>
> --D
>
>> ---
>> fs/xfs/libxfs/xfs_attr.c | 13 +++++--------
>> 1 file changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
>> index fbc9d816882c..6ad50a76fd8d 100644
>> --- a/fs/xfs/libxfs/xfs_attr.c
>> +++ b/fs/xfs/libxfs/xfs_attr.c
>> @@ -1077,21 +1077,18 @@ xfs_attr_node_hasname(
>>
>> state = xfs_da_state_alloc(args);
>> if (statep != NULL)
>> - *statep = NULL;
>> + *statep = state;
>>
>> /*
>> * Search to see if name exists, and get back a pointer to it.
>> */
>> error = xfs_da3_node_lookup_int(state,&retval);
>> - if (error) {
>> - xfs_da_state_free(state);
>> - return error;
>> - }
>> + if (error)
>> + retval = error;
>>
>> - if (statep != NULL)
>> - *statep = state;
>> - else
>> + if (!statep)
>> xfs_da_state_free(state);
>> +
>> return retval;
>> }
>>
>> --
>> 2.23.0
>>