Hi Gang, I don't think this patch is a workaround trick.
We do face the risk using freed iocb although it is actually indeed hard to encounter, it still exists. So I propose to fix it making ocfs2 more reliable. Moreover, this patch has been kept in -mm tree for one month. Can anyone help review it with ack or nack? So I can do some improvement for it. :-) Thanks, Changwei On 04/11/2018 10:51 AM, Gang He wrote: > Hi Changwei, > > The code change just works around the problem, but theoretically the IOCB > object should not be freed before which is handled. > Anyway, if we can find the root cause behind via some way (e.g. inject delay > in some place), the result is more perfect. > > > Thanks > Gang > > >> Hi Jun, >> >> On 2018/4/11 8:52, piaojun wrote: >>> Hi Changwei, >>> >>> It looks like a code bug, and 'iocb' should not be freed at this place. >>> Could this BUG reproduced easily? >> Actually, it's not easy to be reproduced since IO is much slower than CPU >> executing instructions. But the logic here is broken, we'd better fix this. >> >> Thanks, >> Changwei >> >>> thanks, >>> Jun >>> >>> On 2018/4/10 20:00, Changwei Ge wrote: >>>> When -EIOCBQUEUED returns, it means that aio_complete() will be called >>>> from dio_complete(), which is an asynchronous progress against write_iter. >>>> Generally, IO is a very slow progress than executing instruction, but we >>>> still can't take the risk to access a freed iocb. >>>> >>>> And we do face a BUG crash issue. >>>> >From crash tool, iocb is obviously freed already. >>>> crash> struct -x kiocb ffff881a350f5900 >>>> struct kiocb { >>>> ki_filp = 0xffff881a350f5a80, >>>> ki_pos = 0x0, >>>> ki_complete = 0x0, >>>> private = 0x0, >>>> ki_flags = 0x0 >>>> } >>>> >>>> And the backtrace shows: >>>> ocfs2_file_write_iter+0xcaa/0xd00 [ocfs2] >>>> ? ocfs2_check_range_for_refcount+0x150/0x150 [ocfs2] >>>> aio_run_iocb+0x229/0x2f0 >>>> ? try_to_wake_up+0x380/0x380 >>>> do_io_submit+0x291/0x540 >>>> ? syscall_trace_leave+0xad/0x130 >>>> SyS_io_submit+0x10/0x20 >>>> system_call_fastpath+0x16/0x75 >>>> >>>> Signed-off-by: Changwei Ge <ge.chang...@h3c.com> >>>> --- >>>> fs/ocfs2/file.c | 4 ++-- >>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c >>>> index 5d1784a..1393ff2 100644 >>>> --- a/fs/ocfs2/file.c >>>> +++ b/fs/ocfs2/file.c >>>> @@ -2343,7 +2343,7 @@ static ssize_t ocfs2_file_write_iter(struct kiocb >> *iocb, >>>> >>>> written = __generic_file_write_iter(iocb, from); >>>> /* buffered aio wouldn't have proper lock coverage today */ >>>> - BUG_ON(written == -EIOCBQUEUED && !(iocb->ki_flags & IOCB_DIRECT)); >>>> + BUG_ON(written == -EIOCBQUEUED && !direct_io); >>>> >>>> /* >>>> * deep in g_f_a_w_n()->ocfs2_direct_IO we pass in a >>>> ocfs2_dio_end_io >>>> @@ -2463,7 +2463,7 @@ static ssize_t ocfs2_file_read_iter(struct kiocb >>>> *iocb, >>>> trace_generic_file_aio_read_ret(ret); >>>> >>>> /* buffered aio wouldn't have proper lock coverage today */ >>>> - BUG_ON(ret == -EIOCBQUEUED && !(iocb->ki_flags & IOCB_DIRECT)); >>>> + BUG_ON(ret == -EIOCBQUEUED && !direct_io); >>>> >>>> /* see ocfs2_file_write_iter */ >>>> if (ret == -EIOCBQUEUED || !ocfs2_iocb_is_rw_locked(iocb)) { >>>> >> _______________________________________________ >> Ocfs2-devel mailing list >> Ocfs2-devel@oss.oracle.com >> https://oss.oracle.com/mailman/listinfo/ocfs2-devel > > _______________________________________________ > Ocfs2-devel mailing list > Ocfs2-devel@oss.oracle.com > https://oss.oracle.com/mailman/listinfo/ocfs2-devel _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel