From: Linus Torvalds <torvalds@linux-foundation.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Mark Brown <broonie@kernel.org>,
linux-spi <linux-spi@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [GIT PULL] SPI fixes for v5.17-rc7
Date: Tue, 15 Mar 2022 09:48:19 -0700 [thread overview]
Message-ID: <CAHk-=wiZnS6n1ROQg3FHd=bcVTHi-sKutKT+toiViQEH47ZACg@mail.gmail.com> (raw)
In-Reply-To: <CAMuHMdU9t2wLonWBjkXBdxxyK_oJiOUTSqrYVrZWjsY2JKEJ2g@mail.gmail.com>
On Tue, Mar 15, 2022 at 2:08 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> I had noticed while reviewing the patch, but changing to size_t wouldn't
> help much, as other related code paths treat the value as unsigned int
> anyway.
.. but it really would.
Note that the paths *after* this code don't matter. Because the result
is guaranteed to fit in 'unsigned int' anyway.
Put another way:
min_t(unsigned int,x,y)
is buggy if one of x/y is 'size_t'. Why? Because if that one gets
truncated, you're doing 'min()' with a value that may be artificially
much too small (that was exactly the problem commit 1a4e53d2fc4f:
"spi: Fix invalid sgs value")fixed).
But the situation is _not_ true in the reverse. Look:
min(size_t,x,y)
is guaranteed to fit in 'unsigned int' as long as _one_ of x,y fits in
'unsigned int' - even if the other doesn't. Because then 'min()' will
just pick the one that already had the right size.
To make it really concrete, compare
min_t(unsigned int, 5, 0x100000001);
min_t(size_t, 5, 0x100000001);
on a 64-bit machine (ie size_t is 64-bits, and unsigned int is 32-bit).
One returns 1. The other returns 5. Both fit the result in 'unsigned
int', but one of them is wrong.
Linus
next prev parent reply other threads:[~2022-03-15 16:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-10 12:13 [GIT PULL] SPI fixes for v5.17-rc7 Mark Brown
2022-03-10 12:25 ` Linus Torvalds
2022-03-10 12:47 ` Mark Brown
2022-03-15 9:08 ` Geert Uytterhoeven
2022-03-15 16:48 ` Linus Torvalds [this message]
2022-03-15 18:56 ` Geert Uytterhoeven
2022-03-16 16:26 ` Mark Brown
2022-03-16 17:54 ` Biju Das
2022-03-10 12:27 ` pr-tracker-bot
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