On Fri, Feb 07, 2025 at 03:10:33PM +0100, Christian Brauner wrote:
> Before 2011 there was no meaningful synchronization between
> read/readdir/write/seek. Only in commit
> ef3d0fd27e90 ("vfs: do (nearly) lockless generic_file_llseek")
> synchronization was added for SEEK_CUR by taking f_lock around
> vfs_setpos().
>
> Then in 2014 full synchronization between read/readdir/write/seek was
> added in commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX")
> by introducing f_pos_lock for regular files with FMODE_ATOMIC_POS and
> for directories. At that point taking f_lock became unnecessary for such
> files.
>
> So only acquire f_lock for SEEK_CUR if this isn't a file that would have
> acquired f_pos_lock if necessary.
What workloads benefit from this optimisation?
