Dan Williams <dan.j.williams@xxxxxxxxx> writes:
> On Thu, May 12, 2016 at 10:43 AM, Jon Derrick
> <jonathan.derrick@xxxxxxxxx> wrote:
>> When DAX is not compiled into the kernel or the device does not support
>> direct-access, the block device file's inode flags are fully cleared.
>> This patch changes it to only clear the S_DAX flag when DAX is disabled.
>>
>> This reverts to i_flags behavior prior to
>> bbab37ddc20bae4709bca8745c128c4f46fe63c5
>>
>> Signed-off-by: Jon Derrick <jonathan.derrick@xxxxxxxxx>
>> ---
>> fs/block_dev.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/block_dev.c b/fs/block_dev.c
>> index 20a2c02..d4fa725 100644
>> --- a/fs/block_dev.c
>> +++ b/fs/block_dev.c
>> @@ -1208,7 +1208,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
>> if (IS_ENABLED(CONFIG_BLK_DEV_DAX) && disk->fops->direct_access)
>> bdev->bd_inode->i_flags = S_DAX;
>> else
>> - bdev->bd_inode->i_flags = 0;
>> + bdev->bd_inode->i_flags &= ~S_DAX;
>
> Setting S_DAX is atomic, but the above change makes it a non-atomic
> read-modify-write. Do we need exclusion / locking in this path?
First, I don't see how you'd ever get a read-modify-write here, as S_DAX
surely won't ever be set if direct_access isn't supported. Second,
there is existing code that already does this very thing. See further
down in __blkdev_get:
if (!ret) {
bd_set_size(bdev,(loff_t)get_capacity(disk)<<9);
if (!blkdev_dax_capable(bdev))
bdev->bd_inode->i_flags &= ~S_DAX;
}
What relies on S_DAX being set or cleared atomically?
Cheers,
Jeff
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
