On 05/14/2014 12:41 PM, Aravinda Prasad wrote: > > > On Wednesday 14 May 2014 03:42 PM, Jiri Slaby wrote: >> On 05/14/2014 11:28 AM, Aravinda Prasad wrote: >>> On Wednesday 30 April 2014 08:00 PM, Jiri Slaby wrote: >>>> From: Jiri Kosina <jkos...@suse.cz> >>>> >>>> Provide initial implementation. We are now able to do ftrace-based >>>> runtime patching of the kernel code. >>>> >>>> In addition to that, we will provide a kgr_patcher module in the next >>>> patch to test the functionality. >>> >>> Hi Jiri, >>> >>> Interesting! I have couple of comments: >>> >>> I think with kgraft (also with kpatch, though have not looked into >>> it yet), the patched function cannot be dynamically ftraced. >>> Though dynamic ftrace can be enabled on the new code, the user is >>> required to know the function label of the new code. This could >>> potentially break existing scripts. I think this should be documented. >> >> Hi, >> >> of course that the functions can be traced. Look, I turned on tracing >> for capable, then patched, then turned on tracing for new_capable (which >> is the patched function). So now, trace shows: >> console-kit-dae-535 [001] ...1 181.729698: capable <-vt_ioctl >> console-kit-dae-539 [001] ...1 181.729741: capable <-vt_ioctl >> console-kit-dae-541 [000] .N.1 181.906014: capable <-vt_ioctl >> systemd-1 [001] ...1 181.937328: capable <-SyS_epoll_ctl >> sshd-662 [001] ...1 246.437561: capable <-sock_setsockopt >> sshd-662 [001] ...1 246.437564: new_capable >> <-sock_setsockopt >> sshd-662 [001] ...1 246.444790: capable <-sock_setsockopt >> sshd-662 [001] ...1 246.444793: new_capable >> <-sock_setsockopt >> dbus-daemon-128 [000] .N.1 246.456307: capable <-SyS_epoll_ctl >> dbus-daemon-128 [000] ...1 246.456611: new_capable <-SyS_epoll_ctl >> >> >> There is no limitation thanks to the use of the ftrace subsystem. We are >> just another user, i.e. another piece of code called in a loop for a >> particular fentry location. > > Yes true. What I intended to mention is that: the trace is turned on > for "capable" then the function is patched. Eventually, once the patch > is finalized, there will be no trace log for "capable". Someone tracing > the function "capable", not aware of patching, may think that it has not > been invoked. The user, hence, is expected to start tracing > "new_capable". I think this should be documented.
As you can see in the trace log above, no. fentry of capable is still traced (and new_capable is traced along)... > What if someone turns on tracing for "capable" after it is patched? > Will it overwrite the slow/fast stub? Nope, it would look like in the example above. thanks, -- js suse labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
