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bpf: do not update state->loop_entry in get_loop_entry()

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The patch 9 is simpler if less places modify loop_entry field.
The loop deleted by this patch does not affect correctness, but is a
performance optimization. However, measurements on selftests and
sched_ext programs show that this optimization is unnecessary:
- at most 2 steps are done in get_loop_entry();
- most of the time 0 or 1 steps are done in get_loop_entry().

Measured using "do-not-submit" patches from here:
https://github.com/eddyz87/bpf/tree/get-loop-entry-hungup

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250215110411.3236773-8-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Eduard Zingerman 2025-02-15 03:03:58 -08:00 committed by Alexei Starovoitov
parent bb7abf3049
commit 590eee4268
1 changed files with 2 additions and 11 deletions
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13
kernel/bpf/verifier.c
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@ -1829,13 +1829,12 @@ static bool same_callsites(struct bpf_verifier_state *a, struct bpf_verifier_sta
* and cur's loop entry has to be updated (case A), handle this in
* update_branch_counts();
* - use st->branch > 0 as a signal that st is in the current DFS path;
* - handle cases B and C in is_state_visited();
* - update topmost loop entry for intermediate states in get_loop_entry().
* - handle cases B and C in is_state_visited().
*/
static struct bpf_verifier_state *get_loop_entry(struct bpf_verifier_env *env,
struct bpf_verifier_state *st)
{
struct bpf_verifier_state *topmost = st->loop_entry, *old;
struct bpf_verifier_state *topmost = st->loop_entry;
u32 steps = 0;
while (topmost && topmost->loop_entry) {
@ -1846,14 +1845,6 @@ static struct bpf_verifier_state *get_loop_entry(struct bpf_verifier_env *env,
}
topmost = topmost->loop_entry;
}
/* Update loop entries for intermediate states to avoid this
* traversal in future get_loop_entry() calls.
*/
while (st && st->loop_entry != topmost) {
old = st->loop_entry;
st->loop_entry = topmost;
st = old;
}
return topmost;
}