From: Alastair D'Silva <alast...@d-silva.org> The current implementation of TID allocation, using a global IDR, may result in an errant process starving the system of available TIDs. Instead, use task_pid_nr(), as mentioned by the original author. The scenario described which prevented it's use is not applicable, as set_thread_tidr can only be called after the task struct has been populated.
Signed-off-by: Alastair D'Silva <alast...@d-silva.org> --- arch/powerpc/include/asm/switch_to.h | 1 - arch/powerpc/kernel/process.c | 97 +----------------------------------- 2 files changed, 1 insertion(+), 97 deletions(-) diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h index be8c9fa23983..5b03d8a82409 100644 --- a/arch/powerpc/include/asm/switch_to.h +++ b/arch/powerpc/include/asm/switch_to.h @@ -94,6 +94,5 @@ static inline void clear_task_ebb(struct task_struct *t) extern int set_thread_uses_vas(void); extern int set_thread_tidr(struct task_struct *t); -extern void clear_thread_tidr(struct task_struct *t); #endif /* _ASM_POWERPC_SWITCH_TO_H */ diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 3b00da47699b..87f047fd2762 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1496,103 +1496,12 @@ int set_thread_uses_vas(void) } #ifdef CONFIG_PPC64 -static DEFINE_SPINLOCK(vas_thread_id_lock); -static DEFINE_IDA(vas_thread_ida); - -/* - * We need to assign a unique thread id to each thread in a process. - * - * This thread id, referred to as TIDR, and separate from the Linux's tgid, - * is intended to be used to direct an ASB_Notify from the hardware to the - * thread, when a suitable event occurs in the system. - * - * One such event is a "paste" instruction in the context of Fast Thread - * Wakeup (aka Core-to-core wake up in the Virtual Accelerator Switchboard - * (VAS) in POWER9. - * - * To get a unique TIDR per process we could simply reuse task_pid_nr() but - * the problem is that task_pid_nr() is not yet available copy_thread() is - * called. Fixing that would require changing more intrusive arch-neutral - * code in code path in copy_process()?. - * - * Further, to assign unique TIDRs within each process, we need an atomic - * field (or an IDR) in task_struct, which again intrudes into the arch- - * neutral code. So try to assign globally unique TIDRs for now. - * - * NOTE: TIDR 0 indicates that the thread does not need a TIDR value. - * For now, only threads that expect to be notified by the VAS - * hardware need a TIDR value and we assign values > 0 for those. - */ -#define MAX_THREAD_CONTEXT ((1 << 16) - 1) -static int assign_thread_tidr(void) -{ - int index; - int err; - unsigned long flags; - -again: - if (!ida_pre_get(&vas_thread_ida, GFP_KERNEL)) - return -ENOMEM; - - spin_lock_irqsave(&vas_thread_id_lock, flags); - err = ida_get_new_above(&vas_thread_ida, 1, &index); - spin_unlock_irqrestore(&vas_thread_id_lock, flags); - - if (err == -EAGAIN) - goto again; - else if (err) - return err; - - if (index > MAX_THREAD_CONTEXT) { - spin_lock_irqsave(&vas_thread_id_lock, flags); - ida_remove(&vas_thread_ida, index); - spin_unlock_irqrestore(&vas_thread_id_lock, flags); - return -ENOMEM; - } - - return index; -} - -static void free_thread_tidr(int id) -{ - unsigned long flags; - - spin_lock_irqsave(&vas_thread_id_lock, flags); - ida_remove(&vas_thread_ida, id); - spin_unlock_irqrestore(&vas_thread_id_lock, flags); -} - -/* - * Clear any TIDR value assigned to this thread. - */ -void clear_thread_tidr(struct task_struct *t) -{ - if (!t->thread.tidr) - return; - - if (!cpu_has_feature(CPU_FTR_P9_TIDR)) { - WARN_ON_ONCE(1); - return; - } - - mtspr(SPRN_TIDR, 0); - free_thread_tidr(t->thread.tidr); - t->thread.tidr = 0; -} - -void arch_release_task_struct(struct task_struct *t) -{ - clear_thread_tidr(t); -} - /* * Assign a unique TIDR (thread id) for task @t and set it in the thread * structure. For now, we only support setting TIDR for 'current' task. */ int set_thread_tidr(struct task_struct *t) { - int rc; - if (!cpu_has_feature(CPU_FTR_P9_TIDR)) return -EINVAL; @@ -1602,11 +1511,7 @@ int set_thread_tidr(struct task_struct *t) if (t->thread.tidr) return 0; - rc = assign_thread_tidr(); - if (rc < 0) - return rc; - - t->thread.tidr = rc; + t->thread.tidr = (u16)task_pid_nr(t); mtspr(SPRN_TIDR, t->thread.tidr); return 0; -- 2.14.3 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html