Messages in this thread |  | | From | Zach Brown <> | Subject | Re: [PATCH] aio: fix kernel bug when page is temporally busy | Date | Fri, 9 Feb 2007 12:02:08 -0500 |
| |
On Feb 9, 2007, at 6:05 AM, Suparna Bhattacharya wrote:
> On Fri, Feb 09, 2007 at 11:40:27AM +0100, Jiri Kosina wrote: >> On Fri, 9 Feb 2007, Andrew Morton wrote: >> >>>> @@ -1204,7 +1204,7 @@ generic_file_aio_read(struct kiocb *iocb, >>>> const struct iovec *iov, >>>> do_generic_file_read(filp,ppos,&desc,file_read_actor); >>>> retval += desc.written; >>>> if (desc.error) { >>>> - retval = retval ?: desc.error; >>>> + retval = desc.error;
I was worried about this too.
> blocking. The high level AIO code (see aio_rw_vect_rety) has the > ability > to handle this.
I had missed this, and yeah, that's some level of comfort.
But I'm not convinced we can guarantee that's safe. The positive return code that aio_rw_vect_retry() sees is telling it that some IO has completed and, arguably, that no more IO is in flight. If we return partial progress from generic_file_aio_read() while we have an iocb in a wait queue then we are adding yet another invariant. That while an iocb is pending from a previous call down the call chain, we can't return a non-aio negative error. Doing so would cause fs/aio.c to complete while there is still an iocb on a wait queue from a previous retry attempt. Right?
I also noticed something just now while poking around these paths to see if I could get the start of generic_file_aio_read() to fail when it had previously succeeded. What's to stop another task from racing to set O_DIRECT between retries?
That sounds like a pretty hilarious way to get a read retry to fail due to buffer misalignment while a previously buffered instance of it is still in flight. Hi-larious.
In thinking about this a discussing it with Chris a bit, I wonder if the right fix isn't to refuse changing O_DIRECT via setfl() once any IO paths have started on the filp. Something like:
filp->frozen_flags |= O_DIRECT
at the start of paths and check it in setfl()?
Are we similarly worried about O_APPEND?
- z - 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/
|  |