tree ae54ba9fef156271e6cf22c447bd027542e6828a
parent 0074adea39b64d717407b913fd405ac586ee45ca
parent 31f505dc70331243fbb54af868c14bb5f44a15bc
author Linus Torvalds <torvalds@linux-foundation.org> 1737501328 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> 1737501328 -0800
mergetag object 31f505dc70331243fbb54af868c14bb5f44a15bc
 type commit
 tag ftrace-v6.14
 tagger Steven Rostedt (Google) <rostedt@goodmis.org> 1737327700 -0500
 
 ftrace updates for v6.14:
 
 - Have fprobes built on top of function graph infrastructure
 
   The fprobe logic is an optimized kprobe that uses ftrace to attach to
   functions when a probe is needed at the start or end of the function. The
   fprobe and kretprobe logic implements a similar method as the function
   graph tracer to trace the end of the function. That is to hijack the
   return address and jump to a trampoline to do the trace when the function
   exits. To do this, a shadow stack needs to be created to store the
   original return address.  Fprobes and function graph do this slightly
   differently. Fprobes (and kretprobes) has slots per callsite that are
   reserved to save the return address. This is fine when just a few points
   are traced. But users of fprobes, such as BPF programs, are starting to add
   many more locations, and this method does not scale.
 
   The function graph tracer was created to trace all functions in the
   kernel. In order to do this, when function graph tracing is started, every
   task gets its own shadow stack to hold the return address that is going to
   be traced. The function graph tracer has been updated to allow multiple
   users to use its infrastructure. Now have fprobes be one of those users.
   This will also allow for the fprobe and kretprobe methods to trace the
   return address to become obsolete. With new technologies like CFI that
   need to know about these methods of hijacking the return address, going
   toward a solution that has only one method of doing this will make the
   kernel less complex.
 
 - Cleanup with guard() and free() helpers
 
   There were several places in the code that had a lot of "goto out" in the
   error paths to either unlock a lock or free some memory that was
   allocated. But this is error prone. Convert the code over to use the
   guard() and free() helpers that let the compiler unlock locks or free
   memory when the function exits.
 
 - Remove disabling of interrupts in the function graph tracer
 
   When function graph tracer was first introduced, it could race with
   interrupts and NMIs. To prevent that race, it would disable interrupts and
   not trace NMIs. But the code has changed to allow NMIs and also
   interrupts. This change was done a long time ago, but the disabling of
   interrupts was never removed. Remove the disabling of interrupts in the
   function graph tracer is it is not needed. This greatly improves its
   performance.
 
 - Allow the :mod: command to enable tracing module functions on the kernel
   command line.
 
   The function tracer already has a way to enable functions to be traced in
   modules by writing ":mod:<module>" into set_ftrace_filter. That will
   enable either all the functions for the module if it is loaded, or if it
   is not, it will cache that command, and when the module is loaded that
   matches <module>, its functions will be enabled. This also allows init
   functions to be traced. But currently events do not have that feature.
 
   Because enabling function tracing can be done very early at boot up
   (before scheduling is enabled), the commands that can be done when
   function tracing is started is limited. Having the ":mod:" command to
   trace module functions as they are loaded is very useful. Update the
   kernel command line function filtering to allow it.
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Merge tag 'ftrace-v6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull ftrace updates from Steven Rostedt:

 - Have fprobes built on top of function graph infrastructure

   The fprobe logic is an optimized kprobe that uses ftrace to attach to
   functions when a probe is needed at the start or end of the function.
   The fprobe and kretprobe logic implements a similar method as the
   function graph tracer to trace the end of the function. That is to
   hijack the return address and jump to a trampoline to do the trace
   when the function exits. To do this, a shadow stack needs to be
   created to store the original return address. Fprobes and function
   graph do this slightly differently. Fprobes (and kretprobes) has
   slots per callsite that are reserved to save the return address. This
   is fine when just a few points are traced. But users of fprobes, such
   as BPF programs, are starting to add many more locations, and this
   method does not scale.

   The function graph tracer was created to trace all functions in the
   kernel. In order to do this, when function graph tracing is started,
   every task gets its own shadow stack to hold the return address that
   is going to be traced. The function graph tracer has been updated to
   allow multiple users to use its infrastructure. Now have fprobes be
   one of those users. This will also allow for the fprobe and kretprobe
   methods to trace the return address to become obsolete. With new
   technologies like CFI that need to know about these methods of
   hijacking the return address, going toward a solution that has only
   one method of doing this will make the kernel less complex.

 - Cleanup with guard() and free() helpers

   There were several places in the code that had a lot of "goto out" in
   the error paths to either unlock a lock or free some memory that was
   allocated. But this is error prone. Convert the code over to use the
   guard() and free() helpers that let the compiler unlock locks or free
   memory when the function exits.

 - Remove disabling of interrupts in the function graph tracer

   When function graph tracer was first introduced, it could race with
   interrupts and NMIs. To prevent that race, it would disable
   interrupts and not trace NMIs. But the code has changed to allow NMIs
   and also interrupts. This change was done a long time ago, but the
   disabling of interrupts was never removed. Remove the disabling of
   interrupts in the function graph tracer is it is not needed. This
   greatly improves its performance.

 - Allow the :mod: command to enable tracing module functions on the
   kernel command line.

   The function tracer already has a way to enable functions to be
   traced in modules by writing ":mod:<module>" into set_ftrace_filter.
   That will enable either all the functions for the module if it is
   loaded, or if it is not, it will cache that command, and when the
   module is loaded that matches <module>, its functions will be
   enabled. This also allows init functions to be traced. But currently
   events do not have that feature.

   Because enabling function tracing can be done very early at boot up
   (before scheduling is enabled), the commands that can be done when
   function tracing is started is limited. Having the ":mod:" command to
   trace module functions as they are loaded is very useful. Update the
   kernel command line function filtering to allow it.

* tag 'ftrace-v6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (26 commits)
  ftrace: Implement :mod: cache filtering on kernel command line
  tracing: Adopt __free() and guard() for trace_fprobe.c
  bpf: Use ftrace_get_symaddr() for kprobe_multi probes
  ftrace: Add ftrace_get_symaddr to convert fentry_ip to symaddr
  Documentation: probes: Update fprobe on function-graph tracer
  selftests/ftrace: Add a test case for repeating register/unregister fprobe
  selftests: ftrace: Remove obsolate maxactive syntax check
  tracing/fprobe: Remove nr_maxactive from fprobe
  fprobe: Add fprobe_header encoding feature
  fprobe: Rewrite fprobe on function-graph tracer
  s390/tracing: Enable HAVE_FTRACE_GRAPH_FUNC
  ftrace: Add CONFIG_HAVE_FTRACE_GRAPH_FUNC
  bpf: Enable kprobe_multi feature if CONFIG_FPROBE is enabled
  tracing/fprobe: Enable fprobe events with CONFIG_DYNAMIC_FTRACE_WITH_ARGS
  tracing: Add ftrace_fill_perf_regs() for perf event
  tracing: Add ftrace_partial_regs() for converting ftrace_regs to pt_regs
  fprobe: Use ftrace_regs in fprobe exit handler
  fprobe: Use ftrace_regs in fprobe entry handler
  fgraph: Pass ftrace_regs to retfunc
  fgraph: Replace fgraph_ret_regs with ftrace_regs
  ...