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Remove unnecessary RCU grace period chaining #15

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Pull request for series with
subject: Remove unnecessary RCU grace period chaining
version: 1
url: https://patchwork.kernel.org/project/rcu/list/?series=684412

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Master branch: 4b9dfbb
series: https://patchwork.kernel.org/project/rcu/list/?series=684412
version: 1

Pull request is NOT updated. Failed to apply https://patchwork.kernel.org/project/rcu/list/?series=684412
error message:

Cmd('git') failed due to: exit code(128)
  cmdline: git am -3
  stdout: 'Applying: bpf: Free elements after one RCU-tasks-trace grace period
Patch failed at 0001 bpf: Free elements after one RCU-tasks-trace grace period
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".'
  stderr: 'error: sha1 information is lacking or useless (kernel/bpf/memalloc.c).
error: could not build fake ancestor
hint: Use 'git am --show-current-patch=diff' to see the failed patch'

conflict:

@kernel-patches-bot kernel-patches-bot added V2 and removed V1 labels Oct 14, 2022
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

@kernel-patches-bot
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

@kernel-patches-bot
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

@kernel-patches-bot
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

@kernel-patches-bot
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

@kernel-patches-bot
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

@kernel-patches-bot
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

@kernel-patches-bot
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

@kernel-patches-bot
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

@kernel-patches-bot
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

paulmckrcu and others added 4 commits October 20, 2022 09:39
@paulmckrcu @chantra
rcu-tasks: Provide rcu_trace_implies_rcu_gp()
b091a35 
As an accident of implementation, an RCU Tasks Trace grace period also
acts as an RCU grace period.  However, this could change at any time.
This commit therefore creates an rcu_trace_implies_rcu_gp() that currently
returns true to codify this accident.  Code relying on this accident
must call this function to verify that this accident is still happening.

Reported-by: Hou Tao <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
@chantra
bpf: Use rcu_trace_implies_rcu_gp() in bpf memory allocator
213c011 
The memory free logic in bpf memory allocator chains a RCU Tasks Trace
grace period and a normal RCU grace period one after the other, so it
can ensure that both sleepable and non-sleepable programs have finished.

With the introduction of rcu_trace_implies_rcu_gp(),
__free_rcu_tasks_trace() can check whether or not a normal RCU grace
period has also passed after a RCU Tasks Trace grace period has passed.
If it is true, freeing these elements directly, else freeing through
call_rcu().

Signed-off-by: Hou Tao <[email protected]>
@chantra
bpf: Use rcu_trace_implies_rcu_gp() in local storage map
0448657 
Local storage map is accessible for both sleepable and non-sleepable bpf
program, and its memory is freed by using both call_rcu_tasks_trace() and
kfree_rcu() to wait for both RCU-tasks-trace grace period and RCU grace
period to pass.

With the introduction of rcu_trace_implies_rcu_gp(), both
bpf_selem_free_rcu() and bpf_local_storage_free_rcu() can check whether
or not a normal RCU grace period has also passed after a RCU-tasks-trace
grace period has passed. If it is true, it is safe to call kfree()
directly.

Signed-off-by: Hou Tao <[email protected]>
@chantra
bpf: Use rcu_trace_implies_rcu_gp() for program array freeing
32140fa 
To support both sleepable and normal uprobe bpf program, the freeing of
trace program array chains a RCU-tasks-trace grace period and a normal
RCU grace period one after the other.

With the introduction of rcu_trace_implies_rcu_gp(),
__bpf_prog_array_free_sleepable_cb() can check whether or not a normal
RCU grace period has also passed after a RCU-tasks-trace grace period
has passed. If it is true, it is safe to invoke kfree() directly.

Signed-off-by: Hou Tao <[email protected]>
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Master branch: fa70e60
series: https://patchwork.kernel.org/project/rcu/list/?series=685353
version: 2

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@kernel-patches-bot @chantra @paulmckrcu