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221 lines
5.7 KiB
221 lines
5.7 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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#ifndef _LINUX_U64_STATS_SYNC_H |
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#define _LINUX_U64_STATS_SYNC_H |
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/* |
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* Protect against 64-bit values tearing on 32-bit architectures. This is |
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* typically used for statistics read/update in different subsystems. |
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* |
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* Key points : |
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* |
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* - Use a seqcount on 32-bit SMP, only disable preemption for 32-bit UP. |
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* - The whole thing is a no-op on 64-bit architectures. |
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* |
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* Usage constraints: |
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* |
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* 1) Write side must ensure mutual exclusion, or one seqcount update could |
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* be lost, thus blocking readers forever. |
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* |
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* 2) Write side must disable preemption, or a seqcount reader can preempt the |
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* writer and also spin forever. |
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* |
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* 3) Write side must use the _irqsave() variant if other writers, or a reader, |
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* can be invoked from an IRQ context. |
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* |
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* 4) If reader fetches several counters, there is no guarantee the whole values |
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* are consistent w.r.t. each other (remember point #2: seqcounts are not |
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* used for 64bit architectures). |
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* |
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* 5) Readers are allowed to sleep or be preempted/interrupted: they perform |
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* pure reads. |
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* |
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* 6) Readers must use both u64_stats_fetch_{begin,retry}_irq() if the stats |
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* might be updated from a hardirq or softirq context (remember point #1: |
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* seqcounts are not used for UP kernels). 32-bit UP stat readers could read |
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* corrupted 64-bit values otherwise. |
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* |
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* Usage : |
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* |
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* Stats producer (writer) should use following template granted it already got |
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* an exclusive access to counters (a lock is already taken, or per cpu |
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* data is used [in a non preemptable context]) |
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* |
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* spin_lock_bh(...) or other synchronization to get exclusive access |
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* ... |
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* u64_stats_update_begin(&stats->syncp); |
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* u64_stats_add(&stats->bytes64, len); // non atomic operation |
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* u64_stats_inc(&stats->packets64); // non atomic operation |
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* u64_stats_update_end(&stats->syncp); |
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* |
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* While a consumer (reader) should use following template to get consistent |
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* snapshot for each variable (but no guarantee on several ones) |
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* |
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* u64 tbytes, tpackets; |
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* unsigned int start; |
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* |
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* do { |
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* start = u64_stats_fetch_begin(&stats->syncp); |
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* tbytes = u64_stats_read(&stats->bytes64); // non atomic operation |
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* tpackets = u64_stats_read(&stats->packets64); // non atomic operation |
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* } while (u64_stats_fetch_retry(&stats->syncp, start)); |
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* |
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* |
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* Example of use in drivers/net/loopback.c, using per_cpu containers, |
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* in BH disabled context. |
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*/ |
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#include <linux/seqlock.h> |
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struct u64_stats_sync { |
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#if BITS_PER_LONG==32 && defined(CONFIG_SMP) |
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seqcount_t seq; |
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#endif |
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}; |
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#if BITS_PER_LONG == 64 |
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#include <asm/local64.h> |
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typedef struct { |
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local64_t v; |
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} u64_stats_t ; |
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static inline u64 u64_stats_read(const u64_stats_t *p) |
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{ |
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return local64_read(&p->v); |
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} |
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static inline void u64_stats_add(u64_stats_t *p, unsigned long val) |
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{ |
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local64_add(val, &p->v); |
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} |
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static inline void u64_stats_inc(u64_stats_t *p) |
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{ |
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local64_inc(&p->v); |
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} |
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#else |
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typedef struct { |
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u64 v; |
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} u64_stats_t; |
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static inline u64 u64_stats_read(const u64_stats_t *p) |
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{ |
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return p->v; |
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} |
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static inline void u64_stats_add(u64_stats_t *p, unsigned long val) |
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{ |
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p->v += val; |
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} |
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static inline void u64_stats_inc(u64_stats_t *p) |
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{ |
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p->v++; |
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} |
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#endif |
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#if BITS_PER_LONG == 32 && defined(CONFIG_SMP) |
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#define u64_stats_init(syncp) seqcount_init(&(syncp)->seq) |
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#else |
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static inline void u64_stats_init(struct u64_stats_sync *syncp) |
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{ |
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} |
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#endif |
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static inline void u64_stats_update_begin(struct u64_stats_sync *syncp) |
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{ |
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#if BITS_PER_LONG==32 && defined(CONFIG_SMP) |
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write_seqcount_begin(&syncp->seq); |
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#endif |
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} |
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static inline void u64_stats_update_end(struct u64_stats_sync *syncp) |
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{ |
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#if BITS_PER_LONG==32 && defined(CONFIG_SMP) |
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write_seqcount_end(&syncp->seq); |
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#endif |
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} |
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static inline unsigned long |
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u64_stats_update_begin_irqsave(struct u64_stats_sync *syncp) |
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{ |
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unsigned long flags = 0; |
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#if BITS_PER_LONG==32 && defined(CONFIG_SMP) |
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local_irq_save(flags); |
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write_seqcount_begin(&syncp->seq); |
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#endif |
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return flags; |
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} |
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static inline void |
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u64_stats_update_end_irqrestore(struct u64_stats_sync *syncp, |
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unsigned long flags) |
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{ |
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#if BITS_PER_LONG==32 && defined(CONFIG_SMP) |
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write_seqcount_end(&syncp->seq); |
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local_irq_restore(flags); |
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#endif |
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} |
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static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp) |
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{ |
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#if BITS_PER_LONG==32 && defined(CONFIG_SMP) |
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return read_seqcount_begin(&syncp->seq); |
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#else |
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return 0; |
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#endif |
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} |
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static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp) |
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{ |
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#if BITS_PER_LONG==32 && !defined(CONFIG_SMP) |
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preempt_disable(); |
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#endif |
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return __u64_stats_fetch_begin(syncp); |
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} |
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static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp, |
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unsigned int start) |
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{ |
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#if BITS_PER_LONG==32 && defined(CONFIG_SMP) |
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return read_seqcount_retry(&syncp->seq, start); |
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#else |
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return false; |
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#endif |
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} |
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static inline bool u64_stats_fetch_retry(const struct u64_stats_sync *syncp, |
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unsigned int start) |
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{ |
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#if BITS_PER_LONG==32 && !defined(CONFIG_SMP) |
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preempt_enable(); |
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#endif |
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return __u64_stats_fetch_retry(syncp, start); |
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} |
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/* |
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* In case irq handlers can update u64 counters, readers can use following helpers |
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* - SMP 32bit arches use seqcount protection, irq safe. |
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* - UP 32bit must disable irqs. |
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* - 64bit have no problem atomically reading u64 values, irq safe. |
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*/ |
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static inline unsigned int u64_stats_fetch_begin_irq(const struct u64_stats_sync *syncp) |
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{ |
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#if BITS_PER_LONG==32 && !defined(CONFIG_SMP) |
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local_irq_disable(); |
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#endif |
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return __u64_stats_fetch_begin(syncp); |
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} |
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static inline bool u64_stats_fetch_retry_irq(const struct u64_stats_sync *syncp, |
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unsigned int start) |
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{ |
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#if BITS_PER_LONG==32 && !defined(CONFIG_SMP) |
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local_irq_enable(); |
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#endif |
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return __u64_stats_fetch_retry(syncp, start); |
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} |
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#endif /* _LINUX_U64_STATS_SYNC_H */
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