2026年9月12日 08:41, "Zqiang" <[email protected] mailto:[email protected]?to=%22Zqiang%22%20%3Cqiang.zhang%40linux.dev%3E > 写到:
> > > > > On Thu, Sep 10, 2026 at 8:16 PM Zqiang <[email protected]> wrote: > > > > > > From: Kunwu Chan <[email protected]> > > > > This series rounds out atomic SRCU support with a reader-free fastpath, > > some atomic-context fixes, and additional test coverage. > > > > The core change is a reader-free fastpath for synchronize_srcu_atomic(). > > Atomic SRCU's read-side critical sections disable preemption, so when > > the summed lock and unlock counts match for both ranks, > > synchronize_srcu_atomic() can end the grace period immediately, without > > the index flip or the srcu_advance_state() scans. Correctness depends > > on the grace-period anchor written by srcu_gp_start() preceding the > > lock-count scan; two LKMM litmus tests (patches 1-2) verify that > > ordering. > > > > For synchronize_srcu_atomic(), the following items maybe also > > need to be added: > > > > Hi Zqiang > > Sent as: > > https://lore.kernel.org/rcu/[email protected]/ > > > > Did a small late_initcall that enters an atomic read-side critical section > > and > > calls synchronize_srcu_atomic(). srcu_lock_sync() catches it: > > WARNING: possible recursive locking detected > > swapper/0/1 is trying to acquire lock: (&ss) at: > > synchronize_srcu_atomic+0x28/0x380 > > but task is already holding lock: (&ss) at: > > srcu_lockdep_test_init+0xd0/0x170 > > *** DEADLOCK *** > > Rcutorture SRCU-N/P also pass. > > > Hi, kunwu > > You can add srcu_atomic lockdep test to rcutorture to verify > your change, and I also saw that Paul suggested the same thing :) > > For example, as shown below (I am not test or verify it): > > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c > index d795e07a12ad..d4f7399acbd5 100644 > --- a/kernel/rcu/rcutorture.c > +++ b/kernel/rcu/rcutorture.c > @@ -4662,6 +4662,17 @@ static DECLARE_RWSEM(rwsem7); > static DECLARE_RWSEM(rwsem8); > static DECLARE_RWSEM(rwsem9); > > +static DEFINE_RAW_SPINLOCK(spin0); > +static DEFINE_RAW_SPINLOCK(spin1); > +static DEFINE_RAW_SPINLOCK(spin2); > +static DEFINE_RAW_SPINLOCK(spin3); > +static DEFINE_RAW_SPINLOCK(spin4); > +static DEFINE_RAW_SPINLOCK(spin5); > +static DEFINE_RAW_SPINLOCK(spin6); > +static DEFINE_RAW_SPINLOCK(spin7); > +static DEFINE_RAW_SPINLOCK(spin8); > +static DEFINE_RAW_SPINLOCK(spin9); > + > DEFINE_STATIC_SRCU(srcu0); > DEFINE_STATIC_SRCU(srcu1); > DEFINE_STATIC_SRCU(srcu2); > @@ -4673,6 +4684,17 @@ DEFINE_STATIC_SRCU(srcu7); > DEFINE_STATIC_SRCU(srcu8); > DEFINE_STATIC_SRCU(srcu9); > > +DEFINE_STATIC_SRCU_ATOMIC(srcu0_atomic); > +DEFINE_STATIC_SRCU_ATOMIC(srcu1_atomic); > +DEFINE_STATIC_SRCU_ATOMIC(srcu2_atomic); > +DEFINE_STATIC_SRCU_ATOMIC(srcu3_atomic); > +DEFINE_STATIC_SRCU_ATOMIC(srcu4_atomic); > +DEFINE_STATIC_SRCU_ATOMIC(srcu5_atomic); > +DEFINE_STATIC_SRCU_ATOMIC(srcu6_atomic); > +DEFINE_STATIC_SRCU_ATOMIC(srcu7_atomic); > +DEFINE_STATIC_SRCU_ATOMIC(srcu8_atomic); > +DEFINE_STATIC_SRCU_ATOMIC(srcu9_atomic); > + > static int srcu_lockdep_next(const char *f, const char *fl, const char *fs, > const char *fu, int i, > int cyclelen, int deadlock) > { > @@ -4702,6 +4724,13 @@ static void rcu_torture_init_srcu_lockdep(void) > &rwsem5, &rwsem6, &rwsem7, &rwsem8, &rwsem9 }; > struct srcu_struct *srcus[] = { &srcu0, &srcu1, &srcu2, &srcu3, &srcu4, > &srcu5, &srcu6, &srcu7, &srcu8, &srcu9 }; > + > + raw_spinlock_t *spins[] = { &spin0, &spin1, &spin2, &spin3, &spin4, &spin5, > + &spin6, &spin7, &spin8, &spin9}; > + struct srcu_struct *srcus_atomic[] = {&srcu0_atomic, &srcu1_atomic, > &srcu2_atomic, > + &srcu3_atomic, &srcu4_atomic, &srcu5_atomic, > + &srcu6_atomic, &srcu7_atomic, &srcu8_atomic, > + &srcu9_atomic}; > int testtype; > > if (!test_srcu_lockdep) > @@ -4812,11 +4841,48 @@ static void rcu_torture_init_srcu_lockdep(void) > } > #endif // #ifdef CONFIG_TASKS_TRACE_RCU > > + if (testtype == 4) { > + pr_info("%s: test_srcu_lockdep = %05d: SRCU_ATOMIC %d-way %sdeadlock.\n", > + __func__, test_srcu_lockdep, cyclelen, deadlock ? "" : "non-"); > + if (deadlock && cyclelen == 1) > + pr_info("%s: Expect hang.\n", __func__); > + for (i = 0; i < cyclelen; i++) { > + j = srcu_lockdep_next(__func__, "srcu_read_lock_atomic", > "synchronize_srcu_atomic", > + "srcu_read_unlock_atomic", i, cyclelen, deadlock); > + idx = srcu_read_lock_atomic(srcus_atomic[i]); > + if (j >= 0) > + synchronize_srcu_atomic(srcus_atomic[j]); > + srcu_read_unlock_atomic(srcus_atomic[i], idx); > + } > + return; > + } > + > + if (testtype == 1) { ^^^^^^^^ testtype == 5 > + pr_info("%s: test_srcu_lockdep = %05d: SRCU_ATOMIC/raw_spinlock %d-way > %sdeadlock.\n", > + __func__, test_srcu_lockdep, cyclelen, deadlock ? "" : "non-"); > + for (i = 0; i < cyclelen; i++) { > + pr_info("%s: srcu_read_lock_atomic(%d), raw_spin_lock(%d), > raw_spin_unlock(%d), srcu_read_unlock_atomic(%d)\n", > + __func__, i, i, i, i); > + idx = srcu_read_lock_atomic(srcus_atomic[i]); > + raw_spin_lock(spins[i]); > + raw_spin_unlock(spins[i]); > + srcu_read_unlock_atomic(srcus_atomic[i], idx); > + > + j = srcu_lockdep_next(__func__, "raw_spin_lock", "synchronize_srcu_atomic", > + "raw_spin_unlock", i, cyclelen, deadlock); > + raw_spin_lock(spins[i]); > + if (j >= 0) > + synchronize_srcu_atomic(srcus_atomic[j]); > + raw_spin_unlock(spins[i]); > + } > + return; > + } > + > err_out: > pr_info("%s: test_srcu_lockdep = %05d does nothing.\n", __func__, > test_srcu_lockdep); > pr_info("%s: test_srcu_lockdep = DNNL.\n", __func__); > pr_info("%s: D: Deadlock if nonzero.\n", __func__); > - pr_info("%s: NN: Test number, 0=SRCU, 1=SRCU/mutex, 2=SRCU/rwsem, > 3=SRCU/Tasks Trace RCU.\n", __func__); > + pr_info("%s: NN: Test number, 0=SRCU, 1=SRCU/mutex, 2=SRCU/rwsem, > 3=SRCU/Tasks Trace RCU, 4=SRCU_ATOMIC, 5=SRCU_ATOMIC/raw_spinlock.\n", > __func__); > pr_info("%s: L: Cycle length.\n", __func__); > if (!IS_ENABLED(CONFIG_TASKS_TRACE_RCU)) > pr_info("%s: NN=3 disallowed because kernel is built with > CONFIG_TASKS_TRACE_RCU=n\n", __func__); > > Thanks > Zqiang > > > > > Thanks, Kunwu > > > > > > srcu_lock_sync(&ssp->dep_map); > > > > RCU_LOCKDEP_WARN(lockdep_is_held(ssp), > > "Illegal synchronize_srcu() in same-type SRCU read-side critical section"); > > > > if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) > > return; > > > > Thanks > > Zqiang > > > > The series is: > > > > 1-2 LKMM litmus tests for the reader-free fastpath ordering. > > 3 srcutree: add the reader-free fastpath. > > 4 rcutorture: add --do-atomic-srcu to torture.sh. > > 5-7 srcutree: honor and propagate is_atomic so atomic SRCU never > > transitions to big. > > 8 srcutree: forbid srcu_expedite_current() on atomic SRCU. > > 9 rcutorture: disable srcu_expedite_current() for atomic SRCU. > > 10 srcutree: skip callback scheduling for atomic SRCU grace periods. > > 11 srcutree: drop the srcu_barrier() sleep for atomic SRCU. > > 12 srcutree: remove leftover debug pr_alert()s. > > 13 srcu: restrict the non_block annotation to task context, fixing a > > KCSAN data race. > > > > The KCSAN race in patch 13 is a data race on the interrupted task's > > ->non_block_count when a timer callback runs atomic-SRCU readers in > > inline softirq context. > > > > Tested with herd7 7.58 (litmus tests), torture.sh --do-atomic-srcu, and > > torture.sh --do-atomic-srcu --do-kcsan (KCSAN+PROVE_LOCKING). > > > > Kunwu Chan (13): > > litmus: Add SRCU fastpath anchor-before-scan test > > litmus: Add SRCU fastpath scan-before-anchor test > > srcutree: Add reader-free fastpath to synchronize_srcu_atomic() > > rcutorture: Add atomic-SRCU support to torture.sh > > srcutree: Honor is_atomic in check_init_srcu_struct() > > srcutree: Make init_srcu_struct_atomic() prevent transition to big > > srcutree: Don't transition atomic SRCU to big in srcu_gp_end() > > srcutree: Forbid srcu_expedite_current() on atomic SRCU > > rcutorture: Disable srcu_expedite_current() for atomic SRCU > > srcutree: Skip callback scheduling for atomic SRCU grace periods > > srcutree: Remove srcu_barrier() sleep for atomic SRCU > > srcutree: Remove debug pr_alert()s > > srcu: Restrict atomic-SRCU non_block annotation to task context > > > > include/linux/srcu.h | 10 +- > > kernel/rcu/rcutorture.c | 1 + > > kernel/rcu/srcutree.c | 95 ++++++++++++++----- > > tools/memory-model/litmus-tests/README | 16 ++++ > > .../SRCU-fastpath-anchor-before-scan.litmus | 56 +++++++++++ > > .../SRCU-fastpath-scan-before-anchor.litmus | 53 +++++++++++ > > .../selftests/rcutorture/bin/torture.sh | 24 +++++ > > 7 files changed, 229 insertions(+), 26 deletions(-) > > create mode 100644 > > tools/memory-model/litmus-tests/SRCU-fastpath-anchor-before-scan.litmus > > create mode 100644 > > tools/memory-model/litmus-tests/SRCU-fastpath-scan-before-anchor.litmus > > > > base-commit: ef15070f96c5f07de3a9b593c36f6e83bc9e3d58 > > -- > > 2.43.0 > > >
