[EMAIL PROTECTED] wrote on Thursday, December 21, 2006 9:35 AM > kenneth.w.chen> Take ioctx_lock is one part, the other part is to move > kenneth.w.chen> spin_unlock_irqrestore(&ctx->ctx_lock, flags); > kenneth.w.chen> in aio_complete all the way down to the end of the > kenneth.w.chen> function, after wakeup and put_ioctx. But then the ref > kenneth.w.chen> counting on ioctx in aio_complete path is Meaningless, > kenneth.w.chen> which is the thing I'm trying to remove. > > OK, right. But are we simply papering over the real problem? Earlier in > this thread, you stated: > > > flush_workqueue() is not allowed to be called in the softirq context. > > However, aio_complete() called from I/O interrupt can potentially call > > put_ioctx with last ref count on ioctx and trigger a bug warning. It > > is simply incorrect to perform ioctx freeing from aio_complete. > > But how do we end up with the last reference to the ioctx in the aio > completion path? That's a question I haven't seen answered.
It is explained in this posting, A race between io_destroy and aio_complete: http://groups.google.com/group/linux.kernel/msg/d2ba7d73aca1dd0c?&hl=en Trond spotted a bug in that posting. The correct way of locking is to move the spin_unlock_irqrestore in aio_complete all the way down instead of calling aio_put_req at the end. Like this: --- ./fs/aio.c.orig 2006-12-21 08:08:14.000000000 -0800 +++ ./fs/aio.c 2006-12-21 08:14:27.000000000 -0800 @@ -298,17 +298,23 @@ static void wait_for_all_aios(struct kio struct task_struct *tsk = current; DECLARE_WAITQUEUE(wait, tsk); + spin_lock_irq(&ctx->ctx_lock); if (!ctx->reqs_active) - return; + goto out; add_wait_queue(&ctx->wait, &wait); set_task_state(tsk, TASK_UNINTERRUPTIBLE); while (ctx->reqs_active) { + spin_unlock_irq(&ctx->ctx_lock); schedule(); set_task_state(tsk, TASK_UNINTERRUPTIBLE); + spin_lock_irq(&ctx->ctx_lock); } __set_task_state(tsk, TASK_RUNNING); remove_wait_queue(&ctx->wait, &wait); + +out: + spin_unlock_irq(&ctx->ctx_lock); } /* wait_on_sync_kiocb: @@ -424,7 +430,6 @@ static struct kiocb fastcall *__aio_get_ ring = kmap_atomic(ctx->ring_info.ring_pages[0], KM_USER0); if (ctx->reqs_active < aio_ring_avail(&ctx->ring_info, ring)) { list_add(&req->ki_list, &ctx->active_reqs); - get_ioctx(ctx); ctx->reqs_active++; okay = 1; } @@ -536,8 +541,6 @@ int fastcall aio_put_req(struct kiocb *r spin_lock_irq(&ctx->ctx_lock); ret = __aio_put_req(ctx, req); spin_unlock_irq(&ctx->ctx_lock); - if (ret) - put_ioctx(ctx); return ret; } @@ -782,8 +785,7 @@ static int __aio_run_iocbs(struct kioctx */ iocb->ki_users++; /* grab extra reference */ aio_run_iocb(iocb); - if (__aio_put_req(ctx, iocb)) /* drop extra ref */ - put_ioctx(ctx); + __aio_put_req(ctx, iocb); } if (!list_empty(&ctx->run_list)) return 1; @@ -998,14 +1000,10 @@ put_rq: /* everything turned out well, dispose of the aiocb. */ ret = __aio_put_req(ctx, iocb); - spin_unlock_irqrestore(&ctx->ctx_lock, flags); - if (waitqueue_active(&ctx->wait)) wake_up(&ctx->wait); - if (ret) - put_ioctx(ctx); - + spin_unlock_irqrestore(&ctx->ctx_lock, flags); return ret; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
