linux-kernel - Re: aarch64 5.15.68 regression in topology/thread

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Message-ID: <20220922140504.GA58265@meh.true.cz>
Date:   Thu, 22 Sep 2022 16:05:04 +0200
From:   Petr Štetiar <ynezz@...e.cz>
To:     Phil Auld <pauld@...hat.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, yury.norov@...il.com,
        rafael@...nel.org
Subject: Re: aarch64 5.15.68 regression in topology/thread_siblings (huge
 file size and no content)

Phil Auld <pauld@...hat.com> [2022-09-22 09:18:47]:

Hi,

> I've seen the size cause problems for tools. Are we sure that it's the empty file and not
> the size causing issues?  Maybe something is treating that as signed again for a count of
> -1 bytes (which seems like it would be a bug anyway)?

  root@...nWrt:/# strace cat /sys/devices/system/cpu/cpu1/topology/thread_siblings
  ...snip...
  openat(AT_FDCWD, "/sys/devices/system/cpu/cpu1/topology/thread_siblings", O_RDONLY|O_LARGEFILE) = 3
  sendfile(1, 3, NULL, 16777216)          = 0

  root@...nWrt:/# strace md5sum /sys/devices/system/cpu/cpu1/topology/thread_sibli
  ...snip...
  openat(AT_FDCWD, "/sys/devices/system/cpu/cpu1/topology/thread_siblings", O_RDONLY|O_LARGEFILE) = 3
  read(3, "", 4096)                       = 0

  root@...nWrt:/# strace head /sys/devices/system/cpu/cpu1/topology/thread_siblings
  ...snip...
  openat(AT_FDCWD, "/sys/devices/system/cpu/cpu1/topology/thread_siblings", O_RDONLY|O_LARGEFILE) = 3
  read(3, "", 1024)                       = 0

Cheers,

Petr