On Mon, 8 Jun 2020 at 08:07, Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx> wrote: > > Hi Mathieu, Mike > > On 2020-06-04 12:57, Sai Prakash Ranjan wrote: > > > > [...] > > >> > >> Robin has a point - user space is long gone at this time. As such the > >> first > >> question to ask is what kind of CS session was running at the time the > >> system > >> was shutting down. Was it a perf session of a sysfs session? > >> > >> I'm guessing it was a sysfs session because user space has been blown > >> away a > >> while back and part of that process should have killed all perf > >> sessions. > > > > I was enabling trace via sysfs. > > > >> > >> If I am correct then simply switching off the ETR HW in the shutdown() > >> amba bus > >> callback should be fine - otherwise Mike's approach is mandatory. > >> There is > >> also the exchange between Robin and Sai about removing the SMMU > >> shutdown > >> callback, but that thread is still incomplete. > >> > > > > If Robin is hinting at removing SMMU shutdown callback, then I think > > adding > > all these shutdown callbacks to all clients of SMMU can be avoided. Git > > blaming > > the thing shows it was added to avoid some kexec memory corruption. > > > > I think I misread the cryptic hint from Robin and it is not right to > remove > SMMU shutdown callback. For more details on why that was a bad idea and > would > break kexec, please refer to [1]. > > As for the coresight, can I disable the ETR only in the tmc shutdown > callback > or are we still concerned about the userspace coming into picture? User space isn't a concern, especially after you've confirmed the problem occured during an ongoing sysfs session. > > [1] https://lore.kernel.org/patchwork/patch/1253131/ > > Thanks, > Sai > > -- > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a > member > of Code Aurora Forum, hosted by The Linux Foundation
