From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [rdma-rc 13/14] RDMA/mthca: Make explicit conversion to 64bit value Date: Mon, 31 Jul 2017 17:07:32 +0000 Message-ID: <1501520850.2466.17.camel@wdc.com> References: <20170731070924.7193-1-leon@kernel.org> <20170731070924.7193-14-leon@kernel.org> <1501514243.2466.5.camel@wdc.com> <20170731161636.GA13672@mtr-leonro.local> <1501518230.2466.14.camel@wdc.com> <20170731165010.GC13672@mtr-leonro.local> <1501520241.2466.16.camel@wdc.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <1501520241.2466.16.camel-Sjgp3cTcYWE@public.gmane.org> Content-Language: en-US Content-ID: <4214A6662CB5A141B5A2FC1F3CBD5A06-+cFlbfsKLD6cE4WynfumptQqCkab/8FMAL8bYrjMMd8@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org" Cc: "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" List-Id: linux-rdma@vger.kernel.org On Mon, 2017-07-31 at 16:57 +0000, Bart Van Assche wrote: > On Mon, 2017-07-31 at 19:50 +0300, Leon Romanovsky wrote: > > On Mon, Jul 31, 2017 at 04:23:52PM +0000, Bart Van Assche wrote: > > > On Mon, 2017-07-31 at 19:16 +0300, Leon Romanovsky wrote: > > > > On Mon, Jul 31, 2017 at 03:17:24PM +0000, Bart Van Assche wrote: > > > > > On Mon, 2017-07-31 at 10:09 +0300, Leon Romanovsky wrote: > > > > > > From: Leon Romanovsky > > > > > >=20 > > > > > > The "lg" variable is declared as int so in all places where > > > > > > this variable is used as a shift operand, the output will be > > > > > > int too. > > > > > >=20 > > > > > > This produces the following smatch warning: > > > > > > drivers/infiniband/hw/mthca/mthca_cmd.c:701 mthca_map_cmd() war= n: > > > > > > should '1 << lg' be a 64 bit type? > > > > > >=20 > > > > > > Simple declaration of "1" to be "1ULL" will fix the issue. > > > > > >=20 > > > > > > Signed-off-by: Leon Romanovsky > > > > > > Signed-off-by: Leon Romanovsky > > > > > > --- > > > > > > drivers/infiniband/hw/mthca/mthca_cmd.c | 2 +- > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > >=20 > > > > > > diff --git a/drivers/infiniband/hw/mthca/mthca_cmd.c b/drivers/= infiniband/hw/mthca/mthca_cmd.c > > > > > > index 9d83a53c0c67..1052c35f2e75 100644 > > > > > > --- a/drivers/infiniband/hw/mthca/mthca_cmd.c > > > > > > +++ b/drivers/infiniband/hw/mthca/mthca_cmd.c > > > > > > @@ -698,7 +698,7 @@ static int mthca_map_cmd(struct mthca_dev *= dev, u16 op, struct mthca_icm *icm, > > > > > > for (i =3D 0; i < mthca_icm_size(&iter) >> lg; ++i) { > > > > > > if (virt !=3D -1) { > > > > > > pages[nent * 2] =3D cpu_to_be64(virt); > > > > > > - virt +=3D 1 << lg; > > > > > > + virt +=3D 1ULL << lg; > > > > > > } > > > > > >=20 > > > > > > pages[nent * 2 + 1] =3D > > > > >=20 > > > > > Hello Leon, > > > > >=20 > > > > > Is my analysis correct that lg can be equal to or larger than 32?= If so, > > > > > isn't this patch a bug fix that needs a "Fixes:" tag? > > > >=20 > > > > This is the fix to commit introduced in pre-git era and I don't hav= e > > > > adequate Fixes tag. The fact that no one complained about the probl= em > > > > suggests to me that no one is really important to have it in stable= trees. > > > >=20 > > > > Tariq and me did the analysis for the same code issue with mlx4 (he= is > > > > planning to forward the fix to Dave) and our conclusion that it is = not > > > > bug. > > > >=20 > > > > The reason to it in line 689:drivers/infiniband/hw/mthca/mthca_cmd.= c > > > > 689 lg =3D ffs(mthca_icm_addr(&iter) | mthca_icm_s= ize(&iter)) - 1; > > > >=20 > > > > The "lg" for sure will be less than 31, because ffs returns values = from 0 to 31 and minus 1. > > > > The situation that ffs will return 0 is unlikely to happen. > > >=20 > > > Hello Leon, > > >=20 > > > mthca_icm_addr() returns a DMA address (dma_addr_t). Does that mean t= hat > > > that function can return a 64-bit value on 64-bit systems? Shouldn't = ffs() > > > be changed into a function that supports 64-bit values? > >=20 > > Don't dismiss the second part of that ffs: "| mthca_icm_size(&iter)", t= o > > overflow ffs, the icm size should be more than 2^32. Is it real scenari= o? >=20 > The second part of the logical or expression is not relevant if the first= part > can be equal to or larger than 2^32. Has the mthca driver ever been teste= d on > a 64-bit system or should it perhaps be marked as not supporting 64-bit s= ystems? Sorry - I confused ffs() with another instruction. Please ignore my reply. Bart.= -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html