Re: [PATCH v3 11/13] fs: use smp_load_acquire in break_{layout,lease}

[Jeffrey Layton]

On Thu, 2017-10-19 at 19:39 -0700, Dan Williams wrote:
> Commit 128a37852234 "fs: fix data races on inode->i_flctx" converted
> checks of inode->i_flctx to use smp_load_acquire(), but it did not
> convert break_layout(). smp_load_acquire() includes a READ_ONCE(). There
> should be no functional difference since __break_lease repeats the
> sequence, but this is a clean up to unify all ->i_flctx lookups on a
> common pattern.
> 
> Cc: Christoph Hellwig 
> Cc: Alexander Viro 
> Cc: Ross Zwisler 
> Cc: Jeff Layton 
> Cc: "J. Bruce Fields" 
> Signed-off-by: Dan Williams 
> ---
>  include/linux/fs.h |   10 ++
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 13dab191a23e..eace2c5396a7 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2281,8 +2281,9 @@ static inline int break_lease(struct inode *inode, 
> unsigned int mode)
>* could end up racing with tasks trying to set a new lease on this
>* file.
>*/
> - smp_mb();
> - if (inode->i_flctx && !list_empty_careful(>i_flctx->flc_lease))
> + struct file_lock_context *ctx = smp_load_acquire(>i_flctx);
> +
> + if (ctx && !list_empty_careful(>flc_lease))
>   return __break_lease(inode, mode, FL_LEASE);
>   return 0;
>  }
> @@ -2325,8 +2326,9 @@ static inline int break_deleg_wait(struct inode 
> **delegated_inode)
>  
>  static inline int break_layout(struct inode *inode, bool wait)
>  {
> - smp_mb();
> - if (inode->i_flctx && !list_empty_careful(>i_flctx->flc_lease))
> + struct file_lock_context *ctx = smp_load_acquire(>i_flctx);
> +
> + if (ctx && !list_empty_careful(>flc_lease))
>   return __break_lease(inode,
>   wait ? O_WRONLY : O_WRONLY | O_NONBLOCK,
>   FL_LAYOUT);
> 

Nice catch. This can go in independently of the rest of the patches in
the series, I think. I'll assume Andrew is picking this up since he's in
the "To:", but let me know if you need me to get it.

Reviewed-by: Jeff Layton 
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[PATCH v3 11/13] fs: use smp_load_acquire in break_{layout,lease}

[Dan Williams]

Commit 128a37852234 "fs: fix data races on inode->i_flctx" converted
checks of inode->i_flctx to use smp_load_acquire(), but it did not
convert break_layout(). smp_load_acquire() includes a READ_ONCE(). There
should be no functional difference since __break_lease repeats the
sequence, but this is a clean up to unify all ->i_flctx lookups on a
common pattern.

Cc: Christoph Hellwig 
Cc: Alexander Viro 
Cc: Ross Zwisler 
Cc: Jeff Layton 
Cc: "J. Bruce Fields" 
Signed-off-by: Dan Williams 
---
 include/linux/fs.h |   10 ++
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 13dab191a23e..eace2c5396a7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2281,8 +2281,9 @@ static inline int break_lease(struct inode *inode, 
unsigned int mode)
 * could end up racing with tasks trying to set a new lease on this
 * file.
 */
-   smp_mb();
-   if (inode->i_flctx && !list_empty_careful(>i_flctx->flc_lease))
+   struct file_lock_context *ctx = smp_load_acquire(>i_flctx);
+
+   if (ctx && !list_empty_careful(>flc_lease))
return __break_lease(inode, mode, FL_LEASE);
return 0;
 }
@@ -2325,8 +2326,9 @@ static inline int break_deleg_wait(struct inode 
**delegated_inode)
 
 static inline int break_layout(struct inode *inode, bool wait)
 {
-   smp_mb();
-   if (inode->i_flctx && !list_empty_careful(>i_flctx->flc_lease))
+   struct file_lock_context *ctx = smp_load_acquire(>i_flctx);
+
+   if (ctx && !list_empty_careful(>flc_lease))
return __break_lease(inode,
wait ? O_WRONLY : O_WRONLY | O_NONBLOCK,
FL_LAYOUT);

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