| Message ID | 20240930131214.3771313-1-leitao@debian.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | net: netconsole refactoring and warning fix | expand |
On Mon, 30 Sep 2024 06:11:59 -0700 Breno Leitao wrote: > To address these issues, the following steps were taken: > > * Breaking down write_ext_msg() into smaller functions with clear scopes > * Improving readability and reasoning about the code > * Simplifying and clarifying naming conventions > > Warning Fix > ----------- > > The warning occurred when there was insufficient buffer space to append > userdata. While this scenario is acceptable (as userdata can be sent in a > separate packet later), the kernel was incorrectly raising a warning. A > one-line fix has been implemented to resolve this issue. > > A self-test was developed to write messages of every possible length > This test will be submitted in a separate patchset Makes sense in general, but why isn't the fix sent to net first, and then once the trees converge (follow Thursday) we can apply the refactoring and improvements on top? The false positive warning went into 6.9 if I'm checking correctly.
On Thu, Oct 03, 2024 at 05:29:50PM -0700, Jakub Kicinski wrote: > On Mon, 30 Sep 2024 06:11:59 -0700 Breno Leitao wrote: > > To address these issues, the following steps were taken: > > > > * Breaking down write_ext_msg() into smaller functions with clear scopes > > * Improving readability and reasoning about the code > > * Simplifying and clarifying naming conventions > > > > Warning Fix > > ----------- > > > > The warning occurred when there was insufficient buffer space to append > > userdata. While this scenario is acceptable (as userdata can be sent in a > > separate packet later), the kernel was incorrectly raising a warning. A > > one-line fix has been implemented to resolve this issue. > > > > A self-test was developed to write messages of every possible length > > This test will be submitted in a separate patchset > > Makes sense in general, but why isn't the fix sent to net first, > and then once the trees converge (follow Thursday) we can apply > the refactoring and improvements on top? > > The false positive warning went into 6.9 if I'm checking correctly. Correct. I probably should have separated the fix from the refactor. For context, I was pursuing the warning, and the code was hard to read, so, I was refactoring the code while narrowing down the warning. But you are correct, the warning is in 6.9+ kernels. But, keep in mind that the warning is very hard to trigger, basically the length of userdata and the message needs to be certain size to trigger it.
On Fri, 4 Oct 2024 01:50:13 -0700 Breno Leitao wrote: > > Makes sense in general, but why isn't the fix sent to net first, > > and then once the trees converge (follow Thursday) we can apply > > the refactoring and improvements on top? > > > > The false positive warning went into 6.9 if I'm checking correctly. > > Correct. I probably should have separated the fix from the refactor. > > For context, I was pursuing the warning, and the code was hard to read, > so, I was refactoring the code while narrowing down the warning. > > But you are correct, the warning is in 6.9+ kernels. But, keep in mind > that the warning is very hard to trigger, basically the length of userdata > and the message needs to be certain size to trigger it. Understood, and to be honest it's a bit of an efficiency thing on maintainer side - we try to avoid shades of gray as much as possible because debates on what is and isn't a fix can consume a ton of time. So in networking we push people to send the fixes for net, even if triggering the problem isn't very likely.
The netconsole driver was showing a warning related to userdata information, depending on the message size being transmitted: ------------[ cut here ]------------ WARNING: CPU: 13 PID: 3013042 at drivers/net/netconsole.c:1122 write_ext_msg+0x3b6/0x3d0 ? write_ext_msg+0x3b6/0x3d0 console_flush_all+0x1e9/0x330 ... Identifying the cause of this warning proved to be non-trivial due to: * The write_ext_msg() function being over 100 lines long * Extensive use of pointer arithmetic * Inconsistent naming conventions and concept application The send_ext_msg() function grew organically over time: * Initially, the UDP packet consisted of a header and body * Later additions included release prepend and userdata * Naming became inconsistent (e.g., "body" excludes userdata, "header" excludes prepended release) This lack of consistency made investigating issues like the above warning more challenging than what it should be. To address these issues, the following steps were taken: * Breaking down write_ext_msg() into smaller functions with clear scopes * Improving readability and reasoning about the code * Simplifying and clarifying naming conventions Warning Fix ----------- The warning occurred when there was insufficient buffer space to append userdata. While this scenario is acceptable (as userdata can be sent in a separate packet later), the kernel was incorrectly raising a warning. A one-line fix has been implemented to resolve this issue. A self-test was developed to write messages of every possible length This test will be submitted in a separate patchset Changelog: v4: * Pass NULL to userdata in patch 08 ("net: netconsole: do not pass userdata up to the tail") (Simon) * Do not try to read nt->userdata_length outside CONFIG_NETCONSOLE_DYNAMIC in patch 3 ("net: netconsole: separate fragmented message handling in send_ext_msg") (Jakub) * Improve msgbody_written assignment in patch 6 ("net: netconsole: track explicitly if msgbody was written to buffer") (Jakub) v3: * Fix variable definition to an earlier patch (Simon) * Same final code. * https://lore.kernel.org/all/20240910100410.2690012-1-leitao@debian.org/ v2: * Separated the userdata variable move to the tail function into a separated fix (Simon) * Reformated the patches to fit in 80-lines. Only one not respecting this is a copy from previous commit. * https://lore.kernel.org/all/20240909130756.2722126-1-leitao@debian.org/ v1: * https://lore.kernel.org/all/20240903140757.2802765-1-leitao@debian.org/ Breno Leitao (10): net: netconsole: remove msg_ready variable net: netconsole: split send_ext_msg_udp() function net: netconsole: separate fragmented message handling in send_ext_msg net: netconsole: rename body to msg_body net: netconsole: introduce variable to track body length net: netconsole: track explicitly if msgbody was written to buffer net: netconsole: extract release appending into separate function net: netconsole: do not pass userdata up to the tail net: netconsole: split send_msg_fragmented net: netconsole: fix wrong warning drivers/net/netconsole.c | 205 ++++++++++++++++++++++++++------------- 1 file changed, 139 insertions(+), 66 deletions(-)