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Kumar Kartikeya Dwivedi says:
====================
Close race in freeing special fields and map value
There exists a race across various map types where the freeing of
special fields (tw, timer, wq, kptr, etc.) can be done eagerly when a
logical delete operation is done on a map value, such that the program
which continues to have access to such a map value can recreate the
fields and cause them to leak.
The set contains fixes for this case. It is a continuation of Mykyta's
previous attempt in [0], but applies to all fields. A test is included
which reproduces the bug reliably in absence of the fixes.
Local Storage Benchmarks
------------------------
Evaluation Setup: Benchmarked on a dual-socket Intel Xeon Gold 6348 (Ice
Lake) @ 2.60GHz (56 cores / 112 threads), with the CPU governor set to
performance. Bench was pinned to a single NUMA node throughout the test.
Benchmark comes from [1] using the following command:
./bench -p 1 local-storage-create --storage-type <socket,task> --batch-size <16,32,64>
Before the test, 10 runs of all cases ([socket|task] x 3 batch sizes x 7
iterations per batch size) are done to warm up and prime the machine.
Then, 3 runs of all cases are done (with and without the patch, across
reboots).
For each comparison, we have 21 samples, i.e. per batch size (e.g.
socket 16) of a given local storage, we have 3 runs x 7 iterations.
The statistics (mean, median, stddev) and t-test is done for each
scenario (local storage and batch size pair) individually (21 samples
for either case). All values are for local storage creations in thousand
creations / sec (k/s).
Baseline (without patch) With patch Delta
Case Median Mean Std. Dev. Median Mean Std. Dev. Median %
---------------------------------------------------------------------------------------------------
socket 16 432.026 431.941 1.047 431.347 431.953 1.635 -0.679 -0.16%
socket 32 432.641 432.818 1.535 432.488 432.302 1.508 -0.153 -0.04%
socket 64 431.504 431.996 1.337 429.145 430.326 2.469 -2.359 -0.55%
task 16 38.816 39.382 1.456 39.657 39.337 1.831 +0.841 +2.17%
task 32 38.815 39.644 2.690 38.721 39.122 1.636 -0.094 -0.24%
task 64 37.562 38.080 1.701 39.554 38.563 1.689 +1.992 +5.30%
The cases for socket are within the range of noise, and improvements in task
local storage are due to high variance (CV ~4%-6% across batch sizes). The only
statistically significant case worth mentioning is socket with batch size 64
with p-value from t-test < 0.05, but the absolute difference is small (~2k/s).
TL;DR there doesn't appear to be any significant regression or improvement.
[0]: https://lore.kernel.org/bpf/20260216131341.1285427-1-mykyta.yatsenko5@gmail.com
[1]: https://lore.kernel.org/bpf/20260205222916.1788211-1-ameryhung@gmail.com
Changelog:
----------
v2 -> v3
v2: https://lore.kernel.org/bpf/20260227052031.3988575-1-memxor@gmail.com
* Add syzbot Tested-by.
* Add Amery's Reviewed-by.
* Fix missing rcu_dereference_check() in __bpf_selem_free_rcu. (BPF CI Bot)
* Remove migrate_disable() in bpf_selem_free_rcu. (Alexei)
v1 -> v2
v1: https://lore.kernel.org/bpf/20260225185121.2057388-1-memxor@gmail.com
* Add Paul's Reviewed-by.
* Fix use-after-free in accessing bpf_mem_alloc embedded in map. (syzbot CI)
* Add benchmark numbers for local storage.
* Add extra test case for per-cpu hashmap coverage with up to 16 refcount leaks.
* Target bpf tree.
====================
Link: https://patch.msgid.link/20260227224806.646888-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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