On 2019/2/15 17:09, Gao Xiang wrote:
> Hi Chao,
>
> On 2019/2/15 15:29, Chao Yu wrote:
>> On 2019/2/14 23:34, Gao Xiang wrote:
>>> In real scenario, there could be several threads accessing xattrs
>>> of the same xattr-uninitialized inode, and init_inode_xattrs()
>>> almost at the same time.
>>
>> Yeah, nice catch!
>>
>>>
>>> That's actually an unexpected behavior, this patch closes the race.
>>>
>>> Fixes: b17500a0fdba ("staging: erofs: introduce xattr & acl support")
>>> Cc: <[email protected]> # 4.19+
>>> Signed-off-by: Gao Xiang <[email protected]>
>>> ---
>>> drivers/staging/erofs/internal.h | 11 ++++++++---
>>> drivers/staging/erofs/xattr.c | 41
>>> ++++++++++++++++++++++++++++------------
>>> 2 files changed, 37 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/drivers/staging/erofs/internal.h
>>> b/drivers/staging/erofs/internal.h
>>> index 3a27c255950b..e3bfde00c7d2 100644
>>> --- a/drivers/staging/erofs/internal.h
>>> +++ b/drivers/staging/erofs/internal.h
>>> @@ -327,12 +327,17 @@ static inline erofs_off_t iloc(struct erofs_sb_info
>>> *sbi, erofs_nid_t nid)
>>> return blknr_to_addr(sbi->meta_blkaddr) + (nid << sbi->islotbits);
>>> }
>>>
>>> -#define inode_set_inited_xattr(inode) (EROFS_V(inode)->flags |= 1)
>>> -#define inode_has_inited_xattr(inode) (EROFS_V(inode)->flags & 1)
>>> +/* atomic flag definitions */
>>> +#define EROFS_V_EA_INITED_BIT 0
>>> +
>>> +/* bitlock definitions (arranged in reverse order) */
>>> +#define EROFS_V_BL_XATTR_BIT (BITS_PER_LONG - 1)
>>>
>>> struct erofs_vnode {
>>> erofs_nid_t nid;
>>> - unsigned int flags;
>>> +
>>> + /* atomic flags (including bitlocks) */
>>> + unsigned long flags;
>>>
>>> unsigned char data_mapping_mode;
>>> /* inline size in bytes */
>>> diff --git a/drivers/staging/erofs/xattr.c b/drivers/staging/erofs/xattr.c
>>> index 8c48b0ab31fd..a188aad00bf8 100644
>>> --- a/drivers/staging/erofs/xattr.c
>>> +++ b/drivers/staging/erofs/xattr.c
>>> @@ -44,18 +44,25 @@ static inline void xattr_iter_end_final(struct
>>> xattr_iter *it)
>>>
>>> static int init_inode_xattrs(struct inode *inode)
>>> {
>>> + struct erofs_vnode *const vi = EROFS_V(inode);
>>> struct xattr_iter it;
>>> unsigned int i;
>>> struct erofs_xattr_ibody_header *ih;
>>> struct super_block *sb;
>>> struct erofs_sb_info *sbi;
>>> - struct erofs_vnode *vi;
>>> bool atomic_map;
>>> + int ret = 0;
>>>
>>> - if (likely(inode_has_inited_xattr(inode)))
>>> + /* the most case is that xattrs of this inode are initialized. */
>>> + if (likely(test_bit(EROFS_V_EA_INITED_BIT, &vi->flags)))
>>> return 0;
>>>
>>> - vi = EROFS_V(inode);
>>> + if (wait_on_bit_lock(&vi->flags, EROFS_V_BL_XATTR_BIT, TASK_KILLABLE))
>>> + return -ERESTARTSYS;
>>> +
>>> + /* someone has initialized xattrs for us? */
>>> + if (unlikely(test_bit(EROFS_V_EA_INITED_BIT, &vi->flags)))
>>> + goto out_unlock;
>>>
>>> /*
>>> * bypass all xattr operations if ->xattr_isize is not greater than
>>> @@ -68,13 +75,16 @@ static int init_inode_xattrs(struct inode *inode)
>>> if (vi->xattr_isize == sizeof(struct erofs_xattr_ibody_header)) {
>>> errln("xattr_isize %d of nid %llu is not supported yet",
>>> vi->xattr_isize, vi->nid);
>>> - return -ENOTSUPP;
>>> + ret = -ENOTSUPP;
>>> + goto out_unlock;
>>> } else if (vi->xattr_isize < sizeof(struct erofs_xattr_ibody_header)) {
>>> if (unlikely(vi->xattr_isize)) {
>>> DBG_BUGON(1);
>>> - return -EIO; /* xattr ondisk layout error */
>>> + ret = -EIO;
>>> + goto out_unlock; /* xattr ondisk layout error */
>>> }
>>> - return -ENOATTR;
>>> + ret = -ENOATTR;
>>> + goto out_unlock;
>>> }
>>>
>>> sb = inode->i_sb;
>>> @@ -83,8 +93,10 @@ static int init_inode_xattrs(struct inode *inode)
>>> it.ofs = erofs_blkoff(iloc(sbi, vi->nid) + vi->inode_isize);
>>>
>>> it.page = erofs_get_inline_page(inode, it.blkaddr);
>>> - if (IS_ERR(it.page))
>>> - return PTR_ERR(it.page);
>>> + if (IS_ERR(it.page)) {
>>> + ret = PTR_ERR(it.page);
>>> + goto out_unlock;
>>> + }
>>>
>>> /* read in shared xattr array (non-atomic, see kmalloc below) */
>>> it.kaddr = kmap(it.page);
>>> @@ -97,7 +109,8 @@ static int init_inode_xattrs(struct inode *inode)
>>> sizeof(uint), GFP_KERNEL);
>>> if (vi->xattr_shared_xattrs == NULL) {
>>> xattr_iter_end(&it, atomic_map);
>>> - return -ENOMEM;
>>> + ret = -ENOMEM;
>>> + goto out_unlock;
>>> }
>>>
>>> /* let's skip ibody header */
>>> @@ -114,7 +127,8 @@ static int init_inode_xattrs(struct inode *inode)
>>> if (IS_ERR(it.page)) {
>>> kfree(vi->xattr_shared_xattrs);
>>> vi->xattr_shared_xattrs = NULL;
>>> - return PTR_ERR(it.page);
>>> + ret = PTR_ERR(it.page);
>>> + goto out_unlock;
>>> }
>>>
>>> it.kaddr = kmap_atomic(it.page);
>>> @@ -127,8 +141,11 @@ static int init_inode_xattrs(struct inode *inode)
>>> }
>>> xattr_iter_end(&it, atomic_map);
>>>
>>> - inode_set_inited_xattr(inode);
>>> - return 0;
>>> + set_bit(EROFS_V_EA_INITED_BIT, &vi->flags);
>>
>> Should it be?
>>
>> set_bit();
>> wake_up_bit();
>> return 0;
>
> set_bit(EROFS_V_EA_INITED_BIT, &vi->flags); <- set xattrs initialized
> clear_and_wake_up_bit(EROFS_V_BL_XATTR_BIT, &vi->flags); <- clear
> EROFS_V_BL_XATTR_BIT bitlock and wake up waiting tasks...
Yes, you're right, I just missed some points...
Reviewed-by: Chao Yu <[email protected]>
Thanks,
>
> Thanks,
> Gao Xiang
>
>>
>>> +
>>> +out_unlock:
>>> + clear_and_wake_up_bit(EROFS_V_BL_XATTR_BIT, &vi->flags);
>>> + return ret;
>>> }
>>>
>>> /*
>>>
>>
>
> .
>
