On Tue, Aug 01, 2017 at 06:25:56PM +0300, Nikolay Borisov wrote:
> Commit 38851cc19adb ("Btrfs: implement unlocked dio write") implemented
> unlocked dio write, allowing multiple dio writers to write to non-overlapping,
> and non-eof-extending regions. In doing so it also introduced a broken memory
> barrier. It is broken due to 2 things:
>
> 1. Memory barriers _MUST_ always be paired, this is clearly not the case here
>
> 2. Checkpatch actually produces a warning if a memory barrier is introduced that
> doesn't have a comment explaining how it's being paired.
Specifically for inode::i_dio_count that's wrapped inside
inode_dio_begin, there is no explicit barrier semantics attached, so
removing is fine as the atomic is used in common the waiter/wakeup pattern.
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
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