On Fri, 31 Jan 2025 18:06:00 +0900 Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> wrote:
> +static void zram_slot_write_lock(struct zram *zram, u32 index)
> +{
> + atomic_t *lock = &zram->table[index].lock;
> + int old = atomic_read(lock);
> +
> + do {
> + if (old != ZRAM_ENTRY_UNLOCKED) {
> + cond_resched();
> + old = atomic_read(lock);
> + continue;
> + }
> + } while (!atomic_try_cmpxchg(lock, &old, ZRAM_ENTRY_WRLOCKED));
> +}
I expect that if the calling userspace process has realtime policy (eg
SCHED_FIFO) then the cond_resched() won't schedule SCHED_NORMAL tasks
and this becomes a busy loop. And if the machine is single-CPU, the
loop is infinite.
I do agree that for inventing new locking schemes, the bar is set
really high.
