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b=LN5yela/olZJL8Y/saGFEVKcGcaPrLw2aS6Bypl6jX711N5xOrauIe6XVF5khJeAuBiCJvfGqiDUz9623eFLBW2Ihptm8NQzVczelJXGD0ymLkiZRYDgdFsIqPOCJTly/lkOTx+yYMIRJDs2NvmgrF7uiJmG/44N4r8l71SJD2M= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from DS0PR12MB6608.namprd12.prod.outlook.com (2603:10b6:8:d0::10) by IA0PR12MB8973.namprd12.prod.outlook.com (2603:10b6:208:48e::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8048.26; Tue, 15 Oct 2024 05:10:36 +0000 Received: from DS0PR12MB6608.namprd12.prod.outlook.com ([fe80::b71d:8902:9ab3:f627]) by DS0PR12MB6608.namprd12.prod.outlook.com ([fe80::b71d:8902:9ab3:f627%3]) with mapi id 15.20.8048.020; Tue, 15 Oct 2024 05:10:36 +0000 Message-ID: <72ab4701-3d40-42d3-a26a-a0d76fbe27ca@amd.com> Date: Tue, 15 Oct 2024 10:40:27 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH rcu 05/12] srcu: Standardize srcu_data pointers to "sdp" and similar Content-Language: en-US To: paulmck@kernel.org Cc: frederic@kernel.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, Alexei Starovoitov , Andrii Nakryiko , Peter Zijlstra , Kent Overstreet , bpf@vger.kernel.org References: <20241009180719.778285-5-paulmck@kernel.org> <25cd96f1-6d4d-4dba-b57b-da63d228ba97@paulmck-laptop> From: Neeraj Upadhyay In-Reply-To: Content-Type: text/plain; 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McKenney wrote: > On Mon, Oct 14, 2024 at 09:49:52AM -0700, Paul E. McKenney wrote: >> On Mon, Oct 14, 2024 at 02:45:50PM +0530, Neeraj Upadhyay wrote: >>> On 10/9/2024 11:37 PM, Paul E. McKenney wrote: >>>> This commit changes a few "cpuc" variables to "sdp" to align wiht usage >>>> elsewhere. >>>> >>> >>> s/wiht/with/ >> >> Good eyes! > > And fixed. > >>> This commit is doing a lot more than renaming "cpuc". >> >> Indeed, it does look like I forgot to commit between two changes. >> >> It looks like this commit log goes with the changes to the >> functions srcu_readers_lock_idx(), srcu_readers_unlock_idx(), and >> srcu_readers_active(). With the exception of the change from "NMI-safe" >> to "reader flavors in the WARN_ONCE() string in srcu_readers_unlock_idx(). >> >> How would you suggest that I split up the non-s/cpuc/sdp/ changes? > > As a first step, I split it three ways, as you can see on the updated "dev" > branch in the -rcu tree. > > Thoughts? > Split looks good to me! - Neeraj > Thanx, Paul > >>> - Neeraj >>> >>>> Signed-off-by: Paul E. McKenney >>>> Cc: Alexei Starovoitov >>>> Cc: Andrii Nakryiko >>>> Cc: Peter Zijlstra >>>> Cc: Kent Overstreet >>>> Cc: >>>> --- >>>> include/linux/srcu.h | 35 ++++++++++++++++++---------------- >>>> include/linux/srcutree.h | 4 ++++ >>>> kernel/rcu/srcutree.c | 41 ++++++++++++++++++++-------------------- >>>> 3 files changed, 44 insertions(+), 36 deletions(-) >>>> >>>> diff --git a/include/linux/srcu.h b/include/linux/srcu.h >>>> index 06728ef6f32a4..84daaa33ea0ab 100644 >>>> --- a/include/linux/srcu.h >>>> +++ b/include/linux/srcu.h >>>> @@ -176,10 +176,6 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp) >>>> >>>> #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ >>>> >>>> -#define SRCU_NMI_UNKNOWN 0x0 >>>> -#define SRCU_NMI_UNSAFE 0x1 >>>> -#define SRCU_NMI_SAFE 0x2 >>>> - >>>> #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_TREE_SRCU) >>>> void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor); >>>> #else >>>> @@ -235,16 +231,19 @@ static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flav >>>> * a mutex that is held elsewhere while calling synchronize_srcu() or >>>> * synchronize_srcu_expedited(). >>>> * >>>> - * Note that srcu_read_lock() and the matching srcu_read_unlock() must >>>> - * occur in the same context, for example, it is illegal to invoke >>>> - * srcu_read_unlock() in an irq handler if the matching srcu_read_lock() >>>> - * was invoked in process context. >>>> + * The return value from srcu_read_lock() must be passed unaltered >>>> + * to the matching srcu_read_unlock(). Note that srcu_read_lock() and >>>> + * the matching srcu_read_unlock() must occur in the same context, for >>>> + * example, it is illegal to invoke srcu_read_unlock() in an irq handler >>>> + * if the matching srcu_read_lock() was invoked in process context. Or, >>>> + * for that matter to invoke srcu_read_unlock() from one task and the >>>> + * matching srcu_read_lock() from another. >>>> */ >>>> static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp) >>>> { >>>> int retval; >>>> >>>> - srcu_check_read_flavor(ssp, false); >>>> + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL); >>>> retval = __srcu_read_lock(ssp); >>>> srcu_lock_acquire(&ssp->dep_map); >>>> return retval; >>>> @@ -256,12 +255,16 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp) >>>> * >>>> * Enter an SRCU read-side critical section, but in an NMI-safe manner. >>>> * See srcu_read_lock() for more information. >>>> + * >>>> + * If srcu_read_lock_nmisafe() is ever used on an srcu_struct structure, >>>> + * then none of the other flavors may be used, whether before, during, >>>> + * or after. >>>> */ >>>> static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp) >>>> { >>>> int retval; >>>> >>>> - srcu_check_read_flavor(ssp, true); >>>> + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI); >>>> retval = __srcu_read_lock_nmisafe(ssp); >>>> rcu_try_lock_acquire(&ssp->dep_map); >>>> return retval; >>>> @@ -273,7 +276,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp) >>>> { >>>> int retval; >>>> >>>> - srcu_check_read_flavor(ssp, false); >>>> + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL); >>>> retval = __srcu_read_lock(ssp); >>>> return retval; >>>> } >>>> @@ -302,7 +305,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp) >>>> static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp) >>>> { >>>> WARN_ON_ONCE(in_nmi()); >>>> - srcu_check_read_flavor(ssp, false); >>>> + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL); >>>> return __srcu_read_lock(ssp); >>>> } >>>> >>>> @@ -317,7 +320,7 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx) >>>> __releases(ssp) >>>> { >>>> WARN_ON_ONCE(idx & ~0x1); >>>> - srcu_check_read_flavor(ssp, false); >>>> + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL); >>>> srcu_lock_release(&ssp->dep_map); >>>> __srcu_read_unlock(ssp, idx); >>>> } >>>> @@ -333,7 +336,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) >>>> __releases(ssp) >>>> { >>>> WARN_ON_ONCE(idx & ~0x1); >>>> - srcu_check_read_flavor(ssp, true); >>>> + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI); >>>> rcu_lock_release(&ssp->dep_map); >>>> __srcu_read_unlock_nmisafe(ssp, idx); >>>> } >>>> @@ -342,7 +345,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) >>>> static inline notrace void >>>> srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp) >>>> { >>>> - srcu_check_read_flavor(ssp, false); >>>> + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL); >>>> __srcu_read_unlock(ssp, idx); >>>> } >>>> >>>> @@ -359,7 +362,7 @@ static inline void srcu_up_read(struct srcu_struct *ssp, int idx) >>>> { >>>> WARN_ON_ONCE(idx & ~0x1); >>>> WARN_ON_ONCE(in_nmi()); >>>> - srcu_check_read_flavor(ssp, false); >>>> + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL); >>>> __srcu_read_unlock(ssp, idx); >>>> } >>>> >>>> diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h >>>> index ab7d8d215b84b..79ad809c7f035 100644 >>>> --- a/include/linux/srcutree.h >>>> +++ b/include/linux/srcutree.h >>>> @@ -43,6 +43,10 @@ struct srcu_data { >>>> struct srcu_struct *ssp; >>>> }; >>>> >>>> +/* Values for ->srcu_reader_flavor. */ >>>> +#define SRCU_READ_FLAVOR_NORMAL 0x1 // srcu_read_lock(). >>>> +#define SRCU_READ_FLAVOR_NMI 0x2 // srcu_read_lock_nmisafe(). >>>> + >>>> /* >>>> * Node in SRCU combining tree, similar in function to rcu_data. >>>> */ >>>> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c >>>> index abe55777c4335..4c51be484b48a 100644 >>>> --- a/kernel/rcu/srcutree.c >>>> +++ b/kernel/rcu/srcutree.c >>>> @@ -438,9 +438,9 @@ static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx) >>>> unsigned long sum = 0; >>>> >>>> for_each_possible_cpu(cpu) { >>>> - struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); >>>> + struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu); >>>> >>>> - sum += atomic_long_read(&cpuc->srcu_lock_count[idx]); >>>> + sum += atomic_long_read(&sdp->srcu_lock_count[idx]); >>>> } >>>> return sum; >>>> } >>>> @@ -456,14 +456,14 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx) >>>> unsigned long sum = 0; >>>> >>>> for_each_possible_cpu(cpu) { >>>> - struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); >>>> + struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu); >>>> >>>> - sum += atomic_long_read(&cpuc->srcu_unlock_count[idx]); >>>> + sum += atomic_long_read(&sdp->srcu_unlock_count[idx]); >>>> if (IS_ENABLED(CONFIG_PROVE_RCU)) >>>> - mask = mask | READ_ONCE(cpuc->srcu_reader_flavor); >>>> + mask = mask | READ_ONCE(sdp->srcu_reader_flavor); >>>> } >>>> WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask - 1)), >>>> - "Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp); >>>> + "Mixed reader flavors for srcu_struct at %ps.\n", ssp); >>>> return sum; >>>> } >>>> >>>> @@ -564,12 +564,12 @@ static bool srcu_readers_active(struct srcu_struct *ssp) >>>> unsigned long sum = 0; >>>> >>>> for_each_possible_cpu(cpu) { >>>> - struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); >>>> + struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu); >>>> >>>> - sum += atomic_long_read(&cpuc->srcu_lock_count[0]); >>>> - sum += atomic_long_read(&cpuc->srcu_lock_count[1]); >>>> - sum -= atomic_long_read(&cpuc->srcu_unlock_count[0]); >>>> - sum -= atomic_long_read(&cpuc->srcu_unlock_count[1]); >>>> + sum += atomic_long_read(&sdp->srcu_lock_count[0]); >>>> + sum += atomic_long_read(&sdp->srcu_lock_count[1]); >>>> + sum -= atomic_long_read(&sdp->srcu_unlock_count[0]); >>>> + sum -= atomic_long_read(&sdp->srcu_unlock_count[1]); >>>> } >>>> return sum; >>>> } >>>> @@ -703,20 +703,21 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct); >>>> */ >>>> void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) >>>> { >>>> - int reader_flavor_mask = 1 << read_flavor; >>>> - int old_reader_flavor_mask; >>>> + int old_read_flavor; >>>> struct srcu_data *sdp; >>>> >>>> - /* NMI-unsafe use in NMI is a bad sign */ >>>> - WARN_ON_ONCE(!read_flavor && in_nmi()); >>>> + /* NMI-unsafe use in NMI is a bad sign, as is multi-bit read_flavor values. */ >>>> + WARN_ON_ONCE((read_flavor != SRCU_READ_FLAVOR_NMI) && in_nmi()); >>>> + WARN_ON_ONCE(read_flavor & (read_flavor - 1)); >>>> + >>>> sdp = raw_cpu_ptr(ssp->sda); >>>> - old_reader_flavor_mask = READ_ONCE(sdp->srcu_reader_flavor); >>>> - if (!old_reader_flavor_mask) { >>>> - old_reader_flavor_mask = cmpxchg(&sdp->srcu_reader_flavor, 0, reader_flavor_mask); >>>> - if (!old_reader_flavor_mask) >>>> + old_read_flavor = READ_ONCE(sdp->srcu_reader_flavor); >>>> + if (!old_read_flavor) { >>>> + old_read_flavor = cmpxchg(&sdp->srcu_reader_flavor, 0, read_flavor); >>>> + if (!old_read_flavor) >>>> return; >>>> } >>>> - WARN_ONCE(old_reader_flavor_mask != reader_flavor_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_reader_flavor_mask, reader_flavor_mask); >>>> + WARN_ONCE(old_read_flavor != read_flavor, "CPU %d old state %d new state %d\n", sdp->cpu, old_read_flavor, read_flavor); >>>> } >>>> EXPORT_SYMBOL_GPL(srcu_check_read_flavor); >>>> #endif /* CONFIG_PROVE_RCU */ >>>