On Wed, 2016-03-16 at 16:03 +0100, Tomas Henzl wrote:
> On 15.3.2016 22:40, Arnd Bergmann wrote:
> > The qlt_check_reserve_free_req() function produces an incorrect warning
> > when CONFIG_PROFILE_ANNOTATED_BRANCHES is set:
> >
> > drivers/scsi/qla2xxx/qla_target.c: In function 'qlt_check_reserve_free_req':
> > drivers/scsi/qla2xxx/qla_target.c:1887:3: error: 'cnt_in' may be used
> > uninitialized in this function [-Werror=maybe-uninitialized]
> > ql_dbg(ql_dbg_io, vha, 0x305a,
> > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > "qla_target(%d): There is no room in the request ring:
> > vha->req->ring_index=%d, vha->req->cnt=%d, req_cnt=%d Req-out=%d Req-in=%d
> > Req-Length=%d\n",
> >
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > vha->vp_idx, vha->req->ring_index,
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > vha->req->cnt, req_cnt, cnt, cnt_in, vha->req->length);
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > drivers/scsi/qla2xxx/qla_target.c:1887:3: error: 'cnt' may be used
> > uninitialized in this function [-Werror=maybe-uninitialized]
> >
> > The problem is that gcc fails to track the state of the condition across
> > an annotated branch.
> >
> > This slightly rearranges the code to move the second if() block
> > into the first one, to avoid the warning while retaining the
> > behavior of the code.
>
> When the first 'if' is true the vha->req->ring_index gets a new value
> assigned - so it could be possible that the second 'if' wont be true any more.
> The code should not be merged into that single 'if', or am I missing
> something?
>
> tomash
If the first "if" is false, the second "if" will be false also, because
the vha->req->cnt value has not changed. If the first "if" is true, the
nested second "if" will retest the condition.
The compiler is not at fault, because vha->req->cnt can't be tracked as
it could be modified by another thread/process. It isn't, it's protected
by the ->hardware_lock, but the compiler doesn't know that.
-Ewan
> >
> > Signed-off-by: Arnd Bergmann <a...@arndb.de>
> > ---
> > drivers/scsi/qla2xxx/qla_target.c | 16 +++++++++-------
> > 1 file changed, 9 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/scsi/qla2xxx/qla_target.c
> > b/drivers/scsi/qla2xxx/qla_target.c
> > index 985231900aca..8a44d1541eb4 100644
> > --- a/drivers/scsi/qla2xxx/qla_target.c
> > +++ b/drivers/scsi/qla2xxx/qla_target.c
> > @@ -1881,15 +1881,17 @@ static int qlt_check_reserve_free_req(struct
> > scsi_qla_host *vha,
> > else
> > vha->req->cnt = vha->req->length -
> > (vha->req->ring_index - cnt);
> > - }
> >
> > - if (unlikely(vha->req->cnt < (req_cnt + 2))) {
> > - ql_dbg(ql_dbg_io, vha, 0x305a,
> > - "qla_target(%d): There is no room in the request ring:
> > vha->req->ring_index=%d, vha->req->cnt=%d, req_cnt=%d Req-out=%d Req-in=%d
> > Req-Length=%d\n",
> > - vha->vp_idx, vha->req->ring_index,
> > - vha->req->cnt, req_cnt, cnt, cnt_in, vha->req->length);
> > - return -EAGAIN;
> > + if (unlikely(vha->req->cnt < (req_cnt + 2))) {
> > + ql_dbg(ql_dbg_io, vha, 0x305a,
> > + "qla_target(%d): There is no room in the request
> > ring: vha->req->ring_index=%d, vha->req->cnt=%d, req_cnt=%d Req-out=%d
> > Req-in=%d Req-Length=%d\n",
> > + vha->vp_idx, vha->req->ring_index,
> > + vha->req->cnt, req_cnt, cnt, cnt_in,
> > + vha->req->length);
> > + return -EAGAIN;
> > + }
> > }
> > +
> > vha->req->cnt -= req_cnt;
> >
> > return 0;
>
