* Re: [PATCH v1 3/5] treewide: use get_random_u32() when possible
[not found] ` <CAHmME9r_vNRFFjUvqx8QkBddg_kQU=FMgpk9TqOVZdvX6zXHNg@mail.gmail.com>
@ 2022-10-06 13:15 ` Jason Gunthorpe
2022-10-06 13:20 ` Andy Shevchenko
1 sibling, 0 replies; 5+ messages in thread
From: Jason Gunthorpe @ 2022-10-06 13:15 UTC (permalink / raw)
To: Jason A. Donenfeld
Cc: linux-kernel, brcm80211-dev-list.pdl, cake, ceph-devel, coreteam,
dccp, dev, dmaengine, drbd-dev, dri-devel, kasan-dev,
linux-actions, linux-arm-kernel, linux-block, linux-crypto,
linux-doc, linux-ext4, linux-f2fs-devel, linux-fbdev,
linux-fsdevel, linux-hams, linux-media, linux-mm, linux-mmc,
linux-mtd, linux-nfs, linux-nvme, linux-raid, linux-rdma,
linux-scsi, linux-sctp, linux-stm32, linux-usb, linux-wireless,
linux-xfs, linuxppc-dev, lvs-devel, netdev, netfilter-devel,
rds-devel, SHA-cyfmac-dev-list, target-devel, tipc-discussion
On Thu, Oct 06, 2022 at 07:05:48AM -0600, Jason A. Donenfeld wrote:
> > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> > > index fd9d7f2c4d64..a605cf66b83e 100644
> > > --- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> > > +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> > > @@ -465,7 +465,7 @@ static int ipoib_cm_req_handler(struct ib_cm_id *cm_id,
> > > goto err_qp;
> > > }
> > >
> > > - psn = prandom_u32() & 0xffffff;
> > > + psn = get_random_u32() & 0xffffff;
> >
> > prandom_max(0xffffff + 1)
>
> That'd work, but again it's not more clear. Authors here are going for
> a 24-bit number, and masking seems like a clear way to express that.
vs just asking directly for a 24 bit number?
Jason
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v1 3/5] treewide: use get_random_u32() when possible
[not found] ` <CAHmME9r_vNRFFjUvqx8QkBddg_kQU=FMgpk9TqOVZdvX6zXHNg@mail.gmail.com>
2022-10-06 13:15 ` [PATCH v1 3/5] treewide: use get_random_u32() when possible Jason Gunthorpe
@ 2022-10-06 13:20 ` Andy Shevchenko
1 sibling, 0 replies; 5+ messages in thread
From: Andy Shevchenko @ 2022-10-06 13:20 UTC (permalink / raw)
To: Jason A. Donenfeld
Cc: Jason Gunthorpe, linux-kernel, brcm80211-dev-list.pdl, cake,
ceph-devel, coreteam, dccp, dev, dmaengine, drbd-dev, dri-devel,
kasan-dev, linux-actions, linux-arm-kernel, linux-block,
linux-crypto, linux-doc, linux-ext4, linux-f2fs-devel,
linux-fbdev, linux-fsdevel, linux-hams, linux-media, linux-mm,
linux-mmc, linux-mtd, linux-nfs, linux-nvme, linux-raid,
linux-rdma, linux-scsi, linux-sctp, linux-stm32, linux-usb,
linux-wireless, linux-xfs, linuxppc-dev, lvs-devel, netdev,
netfilter-devel, rds-devel, SHA-cyfmac-dev-list, target-devel,
tipc-discussion
On Thu, Oct 06, 2022 at 07:05:48AM -0600, Jason A. Donenfeld wrote:
> On Thu, Oct 6, 2022 at 6:47 AM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > On Wed, Oct 05, 2022 at 11:48:42PM +0200, Jason A. Donenfeld wrote:
...
> > > - u32 isn = (prandom_u32() & ~7UL) - 1;
> > > + u32 isn = (get_random_u32() & ~7UL) - 1;
> >
> > Maybe this wants to be written as
> >
> > (prandom_max(U32_MAX >> 7) << 7) | 7
> > ?
>
> Holy smokes. Yea I guess maybe? It doesn't exactly gain anything or
> make the code clearer though, and is a little bit more magical than
> I'd like on a first pass.
Shouldn't the two first 7s to be 3s?
...
> > > - psn = prandom_u32() & 0xffffff;
> > > + psn = get_random_u32() & 0xffffff;
> >
> > prandom_max(0xffffff + 1)
>
> That'd work, but again it's not more clear. Authors here are going for
> a 24-bit number, and masking seems like a clear way to express that.
We have some 24-bit APIs (and 48-bit) already in kernel, why not to have
get_random_u24() ?
--
With Best Regards,
Andy Shevchenko
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v1 3/5] treewide: use get_random_u32() when possible
[not found] ` <20221005214844.2699-4-Jason@zx2c4.com>
[not found] ` <Yz7OdfKZeGkpZSKb@ziepe.ca>
@ 2022-10-12 19:16 ` Joe Perches
2022-10-12 21:29 ` David Laight
1 sibling, 1 reply; 5+ messages in thread
From: Joe Perches @ 2022-10-12 19:16 UTC (permalink / raw)
To: Jason A. Donenfeld, linux-kernel
Cc: brcm80211-dev-list.pdl, cake, ceph-devel, coreteam, dccp, dev,
dmaengine, drbd-dev, dri-devel, kasan-dev, linux-actions,
linux-arm-kernel, linux-block, linux-crypto, linux-doc,
linux-ext4, linux-f2fs-devel, linux-fbdev, linux-fsdevel,
linux-hams, linux-media, linux-mm, linux-mmc, linux-mtd,
linux-nfs, linux-nvme, linux-raid, linux-rdma, linux-scsi,
linux-sctp, linux-stm32, linux-usb, linux-wireless, linux-xfs,
linuxppc-dev, lvs-devel, netdev, netfilter-devel, rds-devel,
SHA-cyfmac-dev-list, target-devel, tipc-discussion
On Wed, 2022-10-05 at 23:48 +0200, Jason A. Donenfeld wrote:
> The prandom_u32() function has been a deprecated inline wrapper around
> get_random_u32() for several releases now, and compiles down to the
> exact same code. Replace the deprecated wrapper with a direct call to
> the real function.
[]
> diff --git a/drivers/infiniband/hw/cxgb4/cm.c b/drivers/infiniband/hw/cxgb4/cm.c
[]
> @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep)
> &ep->com.remote_addr;
> int ret;
> enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type;
> - u32 isn = (prandom_u32() & ~7UL) - 1;
> + u32 isn = (get_random_u32() & ~7UL) - 1;
trivia:
There are somewhat odd size mismatches here.
I had to think a tiny bit if random() returned a value from 0 to 7
and was promoted to a 64 bit value then truncated to 32 bit.
Perhaps these would be clearer as ~7U and not ~7UL
> struct net_device *netdev;
> u64 params;
>
> @@ -2469,7 +2469,7 @@ static int accept_cr(struct c4iw_ep *ep, struct sk_buff *skb,
> }
>
> if (!is_t4(adapter_type)) {
> - u32 isn = (prandom_u32() & ~7UL) - 1;
> + u32 isn = (get_random_u32() & ~7UL) - 1;
etc...
drivers/infiniband/hw/cxgb4/cm.c: u32 isn = (prandom_u32() & ~7UL) - 1;
drivers/infiniband/hw/cxgb4/cm.c: u32 isn = (prandom_u32() & ~7UL) - 1;
drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c: rpl5->iss = cpu_to_be32((prandom_u32() & ~7UL) - 1);
drivers/scsi/cxgbi/cxgb4i/cxgb4i.c: u32 isn = (prandom_u32() & ~7UL) - 1;
drivers/scsi/cxgbi/cxgb4i/cxgb4i.c: u32 isn = (prandom_u32() & ~7UL) - 1;
drivers/target/iscsi/cxgbit/cxgbit_cm.c: rpl5->iss = cpu_to_be32((prandom_u32() & ~7UL) - 1);
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^ permalink raw reply [flat|nested] 5+ messages in thread
* RE: [PATCH v1 3/5] treewide: use get_random_u32() when possible
2022-10-12 19:16 ` Joe Perches
@ 2022-10-12 21:29 ` David Laight
2022-10-13 1:37 ` Joe Perches
0 siblings, 1 reply; 5+ messages in thread
From: David Laight @ 2022-10-12 21:29 UTC (permalink / raw)
To: 'Joe Perches', Jason A. Donenfeld, linux-kernel
Cc: linux-fbdev, linux-doc, linux-wireless, dri-devel, linux-mm,
linux-sctp, target-devel, linux-mtd, linux-stm32, drbd-dev, dev,
rds-devel, linux-scsi, dccp, linux-rdma, kasan-dev, lvs-devel,
SHA-cyfmac-dev-list, coreteam, tipc-discussion, linux-ext4,
linux-media, linux-actions, linux-nfs, linux-block, dmaengine,
linux-nvme, linux-hams, ceph-devel, linux-arm-kernel, cake,
brcm80211-dev-list.pdl, linux-raid, netdev, linux-usb, linux-mmc,
linux-f2fs-devel, linux-xfs, netfilter-devel, linux-crypto,
linux-fsdevel, linuxppc-dev
From: Joe Perches
> Sent: 12 October 2022 20:17
>
> On Wed, 2022-10-05 at 23:48 +0200, Jason A. Donenfeld wrote:
> > The prandom_u32() function has been a deprecated inline wrapper around
> > get_random_u32() for several releases now, and compiles down to the
> > exact same code. Replace the deprecated wrapper with a direct call to
> > the real function.
> []
> > diff --git a/drivers/infiniband/hw/cxgb4/cm.c b/drivers/infiniband/hw/cxgb4/cm.c
> []
> > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep)
> > &ep->com.remote_addr;
> > int ret;
> > enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type;
> > - u32 isn = (prandom_u32() & ~7UL) - 1;
> > + u32 isn = (get_random_u32() & ~7UL) - 1;
>
> trivia:
>
> There are somewhat odd size mismatches here.
>
> I had to think a tiny bit if random() returned a value from 0 to 7
> and was promoted to a 64 bit value then truncated to 32 bit.
>
> Perhaps these would be clearer as ~7U and not ~7UL
That makes no difference - the compiler will generate the same code.
The real question is WTF is the code doing?
The '& ~7u' clears the bottom 3 bits.
The '- 1' then sets the bottom 3 bits and decrements the
(random) high bits.
So is the same as get_random_u32() | 7.
But I bet the coder had something else in mind.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v1 3/5] treewide: use get_random_u32() when possible
2022-10-12 21:29 ` David Laight
@ 2022-10-13 1:37 ` Joe Perches
0 siblings, 0 replies; 5+ messages in thread
From: Joe Perches @ 2022-10-13 1:37 UTC (permalink / raw)
To: David Laight, Jason A. Donenfeld, linux-kernel
Cc: linux-fbdev, linux-doc, linux-wireless, dri-devel, linux-mm,
linux-sctp, target-devel, linux-mtd, linux-stm32, drbd-dev, dev,
rds-devel, linux-scsi, dccp, linux-rdma, kasan-dev, lvs-devel,
SHA-cyfmac-dev-list, coreteam, tipc-discussion, linux-ext4,
linux-media, linux-actions, linux-nfs, linux-block, dmaengine,
linux-nvme, linux-hams, ceph-devel, linux-arm-kernel, cake,
brcm80211-dev-list.pdl, linux-raid, netdev, linux-usb, linux-mmc,
linux-f2fs-devel, linux-xfs, netfilter-devel, linux-crypto,
linux-fsdevel, linuxppc-dev
On Wed, 2022-10-12 at 21:29 +0000, David Laight wrote:
> From: Joe Perches
> > Sent: 12 October 2022 20:17
> >
> > On Wed, 2022-10-05 at 23:48 +0200, Jason A. Donenfeld wrote:
> > > The prandom_u32() function has been a deprecated inline wrapper around
> > > get_random_u32() for several releases now, and compiles down to the
> > > exact same code. Replace the deprecated wrapper with a direct call to
> > > the real function.
> > []
> > > diff --git a/drivers/infiniband/hw/cxgb4/cm.c b/drivers/infiniband/hw/cxgb4/cm.c
> > []
> > > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep)
> > > &ep->com.remote_addr;
> > > int ret;
> > > enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type;
> > > - u32 isn = (prandom_u32() & ~7UL) - 1;
> > > + u32 isn = (get_random_u32() & ~7UL) - 1;
> >
> > trivia:
> >
> > There are somewhat odd size mismatches here.
> >
> > I had to think a tiny bit if random() returned a value from 0 to 7
> > and was promoted to a 64 bit value then truncated to 32 bit.
> >
> > Perhaps these would be clearer as ~7U and not ~7UL
>
> That makes no difference - the compiler will generate the same code.
True, more or less. It's more a question for the reader.
> The real question is WTF is the code doing?
True.
> The '& ~7u' clears the bottom 3 bits.
> The '- 1' then sets the bottom 3 bits and decrements the
> (random) high bits.
Right.
> So is the same as get_random_u32() | 7.
True, it's effectively the same as the upper 29 bits are random
anyway and the bottom 3 bits are always set.
> But I bet the coder had something else in mind.
Likely.
And it was also likely copy/pasted a few times.
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2022-10-06 13:15 ` [PATCH v1 3/5] treewide: use get_random_u32() when possible Jason Gunthorpe
2022-10-06 13:20 ` Andy Shevchenko
2022-10-12 19:16 ` Joe Perches
2022-10-12 21:29 ` David Laight
2022-10-13 1:37 ` Joe Perches
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