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: <stable@xxxxxxxxxxxxxxx> # 4.19+
>> Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
>> ---
>> 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...
Thanks,
Gao Xiang
>
>> +
>> +out_unlock:
>> + clear_and_wake_up_bit(EROFS_V_BL_XATTR_BIT, &vi->flags);
>> + return ret;
>> }
>>
>> /*
>>
>
