[lustre-devel] [PATCH 15/28] lustre: llite: fix for stat under kthread and X86_X32

[NeilBrown]

On Sun, Oct 14 2018, James Simmons wrote:

> From: Frank Zago <fzago at cray.com>
>
> Under the following conditions, ll_getattr will flatten the inode
> number when it shouldn't:
>
>  - the X86_X32 architecture is defined CONFIG_X86_X32, and not even
>    used,
>  - ll_getattr is called from a kernel thread (though vfs_getattr for
>    instance.)
>
> This has the result that inode numbers are different whether the same
> file is stat'ed from a kernel thread, or from a syscall. For instance,
> 4198401 vs. 144115205272502273.
>
> ll_getattr calls ll_need_32bit_api to determine whether the task is 32
> bits. When the combination is kthread+X86_X32, that function returns
> that the task is 32 bits, which is incorrect, as the kernel is 64
> bits.
>
> The solution is to check whether the call is from a kernel thread
> (which is 64 bits) and act consequently.
>
> Signed-off-by: Frank Zago <fzago at cray.com>
> WC-bug-id: https://jira.whamcloud.com/browse/LU-9468
> Reviewed-on: https://review.whamcloud.com/26992
> Reviewed-by: Andreas Dilger <adilger at whamcloud.com>
> Reviewed-by: Dmitry Eremin <dmitry.eremin at intel.com>
> Signed-off-by: James Simmons <jsimmons at infradead.org>
> ---
>  drivers/staging/lustre/lustre/llite/dir.c          |  6 +++---
>  drivers/staging/lustre/lustre/llite/lcommon_cl.c   |  2 +-
>  .../staging/lustre/lustre/llite/llite_internal.h   | 22 +++++++++++++++++-----
>  3 files changed, 21 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/staging/lustre/lustre/llite/dir.c b/drivers/staging/lustre/lustre/llite/dir.c
> index 231b351..19c5e9c 100644
> --- a/drivers/staging/lustre/lustre/llite/dir.c
> +++ b/drivers/staging/lustre/lustre/llite/dir.c
> @@ -202,7 +202,7 @@ int ll_dir_read(struct inode *inode, __u64 *ppos, struct md_op_data *op_data,
>  {
>  	struct ll_sb_info    *sbi	= ll_i2sbi(inode);
>  	__u64		   pos		= *ppos;
> -	int		   is_api32 = ll_need_32bit_api(sbi);
> +	bool is_api32 = ll_need_32bit_api(sbi);
>  	int		   is_hash64 = sbi->ll_flags & LL_SBI_64BIT_HASH;
>  	struct page	  *page;
>  	bool		   done = false;
> @@ -296,7 +296,7 @@ static int ll_readdir(struct file *filp, struct dir_context *ctx)
>  	struct ll_sb_info	*sbi	= ll_i2sbi(inode);
>  	__u64 pos = lfd ? lfd->lfd_pos : 0;
>  	int			hash64	= sbi->ll_flags & LL_SBI_64BIT_HASH;
> -	int			api32	= ll_need_32bit_api(sbi);
> +	bool api32 = ll_need_32bit_api(sbi);
>  	struct md_op_data *op_data;
>  	int			rc;
>  
> @@ -1674,7 +1674,7 @@ static loff_t ll_dir_seek(struct file *file, loff_t offset, int origin)
>  	struct inode *inode = file->f_mapping->host;
>  	struct ll_file_data *fd = LUSTRE_FPRIVATE(file);
>  	struct ll_sb_info *sbi = ll_i2sbi(inode);
> -	int api32 = ll_need_32bit_api(sbi);
> +	bool api32 = ll_need_32bit_api(sbi);
>  	loff_t ret = -EINVAL;
>  
>  	switch (origin) {
> diff --git a/drivers/staging/lustre/lustre/llite/lcommon_cl.c b/drivers/staging/lustre/lustre/llite/lcommon_cl.c
> index 30f17ea..20a3c74 100644
> --- a/drivers/staging/lustre/lustre/llite/lcommon_cl.c
> +++ b/drivers/staging/lustre/lustre/llite/lcommon_cl.c
> @@ -267,7 +267,7 @@ void cl_inode_fini(struct inode *inode)
>  /**
>   * build inode number from passed @fid
>   */
> -__u64 cl_fid_build_ino(const struct lu_fid *fid, int api32)
> +u64 cl_fid_build_ino(const struct lu_fid *fid, bool api32)
>  {
>  	if (BITS_PER_LONG == 32 || api32)
>  		return fid_flatten32(fid);
> diff --git a/drivers/staging/lustre/lustre/llite/llite_internal.h b/drivers/staging/lustre/lustre/llite/llite_internal.h
> index dcb2fed..796a8ae 100644
> --- a/drivers/staging/lustre/lustre/llite/llite_internal.h
> +++ b/drivers/staging/lustre/lustre/llite/llite_internal.h
> @@ -651,13 +651,25 @@ static inline struct inode *ll_info2i(struct ll_inode_info *lli)
>  __u32 ll_i2suppgid(struct inode *i);
>  void ll_i2gids(__u32 *suppgids, struct inode *i1, struct inode *i2);
>  
> -static inline int ll_need_32bit_api(struct ll_sb_info *sbi)
> +static inline bool ll_need_32bit_api(struct ll_sb_info *sbi)
>  {
>  #if BITS_PER_LONG == 32
> -	return 1;
> +	return true;
>  #elif defined(CONFIG_COMPAT)
> -	return unlikely(in_compat_syscall() ||
> -			(sbi->ll_flags & LL_SBI_32BIT_API));
> +	if (unlikely(sbi->ll_flags & LL_SBI_32BIT_API))
> +		return true;
> +
> +#ifdef CONFIG_X86_X32
> +	/* in_compat_syscall() returns true when called from a kthread
> +	 * and CONFIG_X86_X32 is enabled, which is wrong. So check
> +	 * whether the caller comes from a syscall (ie. not a kthread)
> +	 * before calling in_compat_syscall().
> +	 */
> +	if (current->flags & PF_KTHREAD)
> +		return false;
> +#endif

This is wrong.  We should fix in_compat_syscall(), not work around it
here.
(and then there is that fact that the patch changes 'int' to 'bool'
without explaining that in the change description).

I've sent a query to some relevant people (Cc:ed to James) to ask about
fixing in_compat_syscall().

NeilBrown


> +
> +	return unlikely(in_compat_syscall());
>  #else
>  	return unlikely(sbi->ll_flags & LL_SBI_32BIT_API);
>  #endif
> @@ -1353,7 +1365,7 @@ int cl_setattr_ost(struct cl_object *obj, const struct iattr *attr,
>  int cl_file_inode_init(struct inode *inode, struct lustre_md *md);
>  void cl_inode_fini(struct inode *inode);
>  
> -__u64 cl_fid_build_ino(const struct lu_fid *fid, int api32);
> +u64 cl_fid_build_ino(const struct lu_fid *fid, bool api32);
>  __u32 cl_fid_build_gen(const struct lu_fid *fid);
>  
>  #endif /* LLITE_INTERNAL_H */
> -- 
> 1.8.3.1
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