| Message ID | 20180821113634.3782-1-colin.king@canonical.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/gup_benchmark: fix unsigned comparison with less than zero | expand |
On Tue, Aug 21, 2018 at 11:36:34AM +0000, Colin King wrote: > From: Colin Ian King <colin.king@canonical.com> > > Currently the return from get_user_pages_fast is being checked > to be less than zero for an error check, however, the variable being > checked is unsigned so the check is always false. Fix this by using > a signed long instead. > > Detected by Coccinelle ("Unsigned expression compared with zero: nr <= 0") > > Fixes: 64c349f4ae78 ("mm: add infrastructure for get_user_pages_fast() benchmarking") > Signed-off-by: Colin Ian King <colin.king@canonical.com> This is good catch, but the fix is wrong. See below. > --- > mm/gup_benchmark.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c > index 6a473709e9b6..a9a15e7a1185 100644 > --- a/mm/gup_benchmark.c > +++ b/mm/gup_benchmark.c > @@ -31,6 +31,8 @@ static int __gup_benchmark_ioctl(unsigned int cmd, > nr = gup->nr_pages_per_call; > start_time = ktime_get(); > for (addr = gup->addr; addr < gup->addr + gup->size; addr = next) { > + long n; > + > if (nr != gup->nr_pages_per_call) > break; This check has to be done against 'n', not nr'. We stop as soon as get_user_pages_fast() doesn't return the number of pages we expected. I would rather change type of 'nr' to signed. It should also fix the issue, right?
diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c index 6a473709e9b6..a9a15e7a1185 100644 --- a/mm/gup_benchmark.c +++ b/mm/gup_benchmark.c @@ -31,6 +31,8 @@ static int __gup_benchmark_ioctl(unsigned int cmd, nr = gup->nr_pages_per_call; start_time = ktime_get(); for (addr = gup->addr; addr < gup->addr + gup->size; addr = next) { + long n; + if (nr != gup->nr_pages_per_call) break; @@ -40,10 +42,10 @@ static int __gup_benchmark_ioctl(unsigned int cmd, nr = (next - addr) / PAGE_SIZE; } - nr = get_user_pages_fast(addr, nr, gup->flags & 1, pages + i); - if (nr <= 0) + n = get_user_pages_fast(addr, nr, gup->flags & 1, pages + i); + if (n <= 0) break; - i += nr; + i += n; } end_time = ktime_get();