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McKenney writes: > On Wed, Feb 14, 2024 at 07:45:18PM -0800, Paul E. McKenney wrote: >> On Wed, Feb 14, 2024 at 06:03:28PM -0800, Ankur Arora wrote: >> > >> > Paul E. McKenney writes: >> > >> > > On Mon, Feb 12, 2024 at 09:55:24PM -0800, Ankur Arora wrote: >> > >> Hi, >> > >> >> > >> This series adds a new scheduling model PREEMPT_AUTO, which like >> > >> PREEMPT_DYNAMIC allows dynamic switching between a none/voluntary/full >> > >> preemption model. However, unlike PREEMPT_DYNAMIC, it doesn't depend >> > >> on explicit preemption points for the voluntary models. >> > >> >> > >> The series is based on Thomas' original proposal which he outlined >> > >> in [1], [2] and in his PoC [3]. >> > >> >> > >> An earlier RFC version is at [4]. >> > > >> > > This uncovered a couple of latent bugs in RCU due to its having been >> > > a good long time since anyone built a !SMP preemptible kernel with >> > > non-preemptible RCU. I have a couple of fixes queued on -rcu [1], most >> > > likely for the merge window after next, but let me know if you need >> > > them sooner. >> > >> > Thanks. As you can probably tell, I skipped out on !SMP in my testing. >> > But, the attached diff should tide me over until the fixes are in. >> >> That was indeed my guess. ;-) >> >> > > I am also seeing OOM conditions during rcutorture testing of callback >> > > flooding, but I am still looking into this. >> > >> > That's on the PREEMPT_AUTO && PREEMPT_VOLUNTARY configuration? >> >> On two of the PREEMPT_AUTO && PREEMPT_NONE configurations, but only on >> two of them thus far. I am running a longer test to see if this might >> be just luck. If not, I look to see what rcutorture scenarios TREE10 >> and TRACE01 have in common. > > And still TRACE01 and TREE10 are hitting OOMs, still not seeing what > sets them apart. I also hit a grace-period hang in TREE04, which does > CONFIG_PREEMPT_VOLUNTARY=y along with CONFIG_PREEMPT_AUTO=y. Something > to dig into more. > > I am also getting these from builds that enable KASAN: > > vmlinux.o: warning: objtool: mwait_idle+0x13: call to tif_resched.constprop.0() leaves .noinstr.text section > vmlinux.o: warning: objtool: acpi_processor_ffh_cstate_enter+0x36: call to tif_resched.constprop.0() leaves .noinstr.text section > vmlinux.o: warning: objtool: cpu_idle_poll.isra.0+0x18: call to tif_resched.constprop.0() leaves .noinstr.text section > vmlinux.o: warning: objtool: acpi_safe_halt+0x0: call to tif_resched.constprop.0() leaves .noinstr.text section > vmlinux.o: warning: objtool: poll_idle+0x33: call to tif_resched.constprop.0() leaves .noinstr.text section > vmlinux.o: warning: objtool: default_enter_idle+0x18: call to tif_resched.constprop.0() leaves .noinstr.text section Thanks Paul. Yeah, with KASAN, tif_resched() transforms into this out of line function: ffffffff810fec20 : ffffffff810fec20: e8 5b c6 20 00 call ffffffff8130b280 <__sanitizer_cov_trace_pc> ffffffff810fec25: b8 03 00 00 00 mov $0x3,%eax ffffffff810fec2a: e9 71 56 61 01 jmp ffffffff827142a0 <__x86_return_thunk> ffffffff810fec2f: 90 nop > Does tif_resched() need to be marked noinstr or some such? Builds fine with Thomas' suggested fix. -------- diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h index 8752dbc2dac7..0810ddeb365d 100644 --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -81,12 +81,12 @@ typedef enum { * reduce to the same value (TIF_NEED_RESCHED) leaving any scheduling behaviour * unchanged. */ -static inline int tif_resched(resched_t rs) +static __always_inline inline int tif_resched(resched_t rs) { return TIF_NEED_RESCHED + rs * TIF_NEED_RESCHED_LAZY_OFFSET; } -static inline int _tif_resched(resched_t rs) +static __always_inline inline int _tif_resched(resched_t rs) { return 1 << tif_resched(rs); }