On Wed, 18 Dec 2024 07:43:46 +0800 Edward Adam Davis <eada...@qq.com> wrote:
> > > > A proper fix is being discussed here: > First, my fix is the first one. Yes I saw that. > Second, the root cause of the problem is an overflow when calculating > nr_pages. > > > > https://lore.kernel.org/linux-trace-kernel/20241216164931.57323-1-aha310...@gmail.com/ > > > > Thank you, > > > > -- Steve > > > The calculation of nr_pages below overflows because the pgoff value is 8, > the nr_subbufs value is 3, and the subbuf_order value is 0. So basically you are saying that passing in the the mmap with the pgoff is what's causing it. > > > nr_pages = ((nr_subbufs + 1) << subbuf_order) - pgoff; /* + meta-page */ > > > > > > nr_vma_pages = vma_pages(vma); Thanks, I believe I now have a reproducer. And yes, I'll take your patch. (If Vincent is OK with it). Here's the reproducer: ------------------------8<------------------------- #include <fcntl.h> #include <stdlib.h> #include <unistd.h> #include <asm/types.h> #include <sys/mman.h> int main(int argc, char **argv) { int page_size = getpagesize(); int fd; void *meta; system("echo 1 > /sys/kernel/tracing/buffer_size_kb"); fd = open("/sys/kernel/tracing/per_cpu/cpu0/trace_pipe_raw", O_RDONLY); meta = mmap(NULL, page_size, PROT_READ, MAP_SHARED, fd, page_size * 5); } ------------------------>8------------------------- Thanks, -- Steve
