Thanks for reviewing, I added some questions inline below
On Mon, Jul 27, 2020 at 7:21 AM Alexey Dobriyan [off-list ref] wrote:
quoted
+ d = strndup_user(desc, MAX_FILE_DESC_SIZE);
This should be kmem accounted because allocation is persistent.
To make things more entertaining, strndup_user() doesn't have gfp_t argument.
I had to look it up so I might be very far from it, but is that
__GFP_ACCOUNT and would it be correct to assume memdup_user() should
use it unconditionally?
Otherwise my simple option would be to implement the logic in the
set_description, but the benefit would be very local.
Please let me know what you think is best, happy to read more doc if
there's a more productive way to address that
quoted
+ if (IS_ERR(d))
+ return PTR_ERR(d);
+
+ spin_lock(&file->f_lock);
+ kfree(file->f_description);
+ file->f_description = d;
+ spin_unlock(&file->f_lock);
Generally kfree under spinlock is not good idea.
You can replace the pointer and free without spinlock.
Sorry I also need some pointers here - do you suggest I move the kfree
out of the locked section or that there is a safe way other than
spinlock?
struct file is nicely aligned to 256 bytes on distro configs.
Will this break everything?
$ cat /sys/kernel/slab/filp/object_size
Indeed on the config I'm using here this jumped to 264 bytes
Would it be better to move this to the inode struct? I don't know the
implications of this - any other option?
Thanks!