Messages in this thread Patch in this message | | | From | "Chen, Kenneth W" <> | Subject | RE: 2.6.18.4: flush_workqueue calls mutex_lock in interrupt environment | Date | Thu, 14 Dec 2006 22:35:07 -0800 |
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Chen, Kenneth wrote on Thursday, December 14, 2006 5:59 PM > > It seems utterly insane to have aio_complete() flush a workqueue. That > > function has to be called from a number of different environments, > > including non-sleep tolerant environments. > > > > For instance it means that directIO on NFS will now cause the rpciod > > workqueues to call flush_workqueue(aio_wq), thus slowing down all RPC > > activity. > > The bug appears to be somewhere else, somehow the ref count on ioctx is > all messed up. > > In aio_complete, __put_ioctx() should not be invoked because ref count > on ioctx is supposedly more than 2, aio_complete decrement it once and > should return without invoking the free function. > > The real freeing ioctx should be coming from exit_aio() or io_destroy(), > in which case both wait until no further pending AIO request via > wait_for_all_aios().
Ah, I think I see the bug: it must be a race between io_destroy() and aio_complete(). A possible scenario:
cpu0 cpu1 io_destroy aio_complete wait_for_all_aios { __aio_put_req ... ctx->reqs_active--; if (!ctx->reqs_active) return; } ... put_ioctx(ioctx)
put_ioctx(ctx); bam! Bug trigger!
AIO finished on cpu1 and while in the middle of aio_complete, cpu0 starts io_destroy sequence, sees no pending AIO, went ahead decrement the ref count on ioctx. At a later point in aio_complete, the put_ioctx decrement last ref count and calls the ioctx freeing function and there it triggered the bug warning.
A simple fix would be to access ctx->reqs_active inside ctx spin lock in wait_for_all_aios(). At the mean time, I would like to remove ref counting for each iocb because we already performing ref count using reqs_active. This would also prevent similar buggy code in the future.
Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
--- ./fs/aio.c.orig 2006-11-29 13:57:37.000000000 -0800 +++ ./fs/aio.c 2006-12-14 20:45:14.000000000 -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: @@ -425,7 +431,6 @@ 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; } @@ -538,8 +543,6 @@ 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; } @@ -795,8 +798,7 @@ 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; @@ -942,7 +944,6 @@ int fastcall aio_complete(struct kiocb * struct io_event *event; unsigned long flags; unsigned long tail; - int ret; /* * Special case handling for sync iocbs: @@ -1011,18 +1012,12 @@ int fastcall aio_complete(struct kiocb * pr_debug("%ld retries: %zd of %zd\n", iocb->ki_retried, iocb->ki_nbytes - iocb->ki_left, iocb->ki_nbytes); 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); - - return ret; + return aio_put_req(iocb); } /* aio_read_evt - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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