mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-04 18:09:57 +00:00
![Peter Zijlstra](/assets/img/avatar_default.png)
Jakub reported that: static struct net_device *rtl8139_init_board(struct pci_dev *pdev) { ... u64_stats_init(&tp->rx_stats.syncp); u64_stats_init(&tp->tx_stats.syncp); ... } results in lockdep getting confused between the RX and TX stats lock. This is because u64_stats_init() is an inline calling seqcount_init(), which is a macro using a static variable to generate a lockdep class. By wrapping that in an inline, we negate the effect of the macro and fold the static key variable, hence the confusion. Fix by also making u64_stats_init() a macro for the case where it matters, leaving the other case an inline for argument validation etc. Reported-by: Jakub Kicinski <kuba@kernel.org> Debugged-by: "Ahmed S. Darwish" <a.darwish@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: "Erhard F." <erhard_f@mailbox.org> Link: https://lkml.kernel.org/r/YEXicy6+9MksdLZh@hirez.programming.kicks-ass.net
221 lines
5.7 KiB
C
221 lines
5.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
#ifndef _LINUX_U64_STATS_SYNC_H
|
|
#define _LINUX_U64_STATS_SYNC_H
|
|
|
|
/*
|
|
* Protect against 64-bit values tearing on 32-bit architectures. This is
|
|
* typically used for statistics read/update in different subsystems.
|
|
*
|
|
* Key points :
|
|
*
|
|
* - Use a seqcount on 32-bit SMP, only disable preemption for 32-bit UP.
|
|
* - The whole thing is a no-op on 64-bit architectures.
|
|
*
|
|
* Usage constraints:
|
|
*
|
|
* 1) Write side must ensure mutual exclusion, or one seqcount update could
|
|
* be lost, thus blocking readers forever.
|
|
*
|
|
* 2) Write side must disable preemption, or a seqcount reader can preempt the
|
|
* writer and also spin forever.
|
|
*
|
|
* 3) Write side must use the _irqsave() variant if other writers, or a reader,
|
|
* can be invoked from an IRQ context.
|
|
*
|
|
* 4) If reader fetches several counters, there is no guarantee the whole values
|
|
* are consistent w.r.t. each other (remember point #2: seqcounts are not
|
|
* used for 64bit architectures).
|
|
*
|
|
* 5) Readers are allowed to sleep or be preempted/interrupted: they perform
|
|
* pure reads.
|
|
*
|
|
* 6) Readers must use both u64_stats_fetch_{begin,retry}_irq() if the stats
|
|
* might be updated from a hardirq or softirq context (remember point #1:
|
|
* seqcounts are not used for UP kernels). 32-bit UP stat readers could read
|
|
* corrupted 64-bit values otherwise.
|
|
*
|
|
* Usage :
|
|
*
|
|
* Stats producer (writer) should use following template granted it already got
|
|
* an exclusive access to counters (a lock is already taken, or per cpu
|
|
* data is used [in a non preemptable context])
|
|
*
|
|
* spin_lock_bh(...) or other synchronization to get exclusive access
|
|
* ...
|
|
* u64_stats_update_begin(&stats->syncp);
|
|
* u64_stats_add(&stats->bytes64, len); // non atomic operation
|
|
* u64_stats_inc(&stats->packets64); // non atomic operation
|
|
* u64_stats_update_end(&stats->syncp);
|
|
*
|
|
* While a consumer (reader) should use following template to get consistent
|
|
* snapshot for each variable (but no guarantee on several ones)
|
|
*
|
|
* u64 tbytes, tpackets;
|
|
* unsigned int start;
|
|
*
|
|
* do {
|
|
* start = u64_stats_fetch_begin(&stats->syncp);
|
|
* tbytes = u64_stats_read(&stats->bytes64); // non atomic operation
|
|
* tpackets = u64_stats_read(&stats->packets64); // non atomic operation
|
|
* } while (u64_stats_fetch_retry(&stats->syncp, start));
|
|
*
|
|
*
|
|
* Example of use in drivers/net/loopback.c, using per_cpu containers,
|
|
* in BH disabled context.
|
|
*/
|
|
#include <linux/seqlock.h>
|
|
|
|
struct u64_stats_sync {
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
seqcount_t seq;
|
|
#endif
|
|
};
|
|
|
|
#if BITS_PER_LONG == 64
|
|
#include <asm/local64.h>
|
|
|
|
typedef struct {
|
|
local64_t v;
|
|
} u64_stats_t ;
|
|
|
|
static inline u64 u64_stats_read(const u64_stats_t *p)
|
|
{
|
|
return local64_read(&p->v);
|
|
}
|
|
|
|
static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
|
|
{
|
|
local64_add(val, &p->v);
|
|
}
|
|
|
|
static inline void u64_stats_inc(u64_stats_t *p)
|
|
{
|
|
local64_inc(&p->v);
|
|
}
|
|
|
|
#else
|
|
|
|
typedef struct {
|
|
u64 v;
|
|
} u64_stats_t;
|
|
|
|
static inline u64 u64_stats_read(const u64_stats_t *p)
|
|
{
|
|
return p->v;
|
|
}
|
|
|
|
static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
|
|
{
|
|
p->v += val;
|
|
}
|
|
|
|
static inline void u64_stats_inc(u64_stats_t *p)
|
|
{
|
|
p->v++;
|
|
}
|
|
#endif
|
|
|
|
#if BITS_PER_LONG == 32 && defined(CONFIG_SMP)
|
|
#define u64_stats_init(syncp) seqcount_init(&(syncp)->seq)
|
|
#else
|
|
static inline void u64_stats_init(struct u64_stats_sync *syncp)
|
|
{
|
|
}
|
|
#endif
|
|
|
|
static inline void u64_stats_update_begin(struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
write_seqcount_begin(&syncp->seq);
|
|
#endif
|
|
}
|
|
|
|
static inline void u64_stats_update_end(struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
write_seqcount_end(&syncp->seq);
|
|
#endif
|
|
}
|
|
|
|
static inline unsigned long
|
|
u64_stats_update_begin_irqsave(struct u64_stats_sync *syncp)
|
|
{
|
|
unsigned long flags = 0;
|
|
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
local_irq_save(flags);
|
|
write_seqcount_begin(&syncp->seq);
|
|
#endif
|
|
return flags;
|
|
}
|
|
|
|
static inline void
|
|
u64_stats_update_end_irqrestore(struct u64_stats_sync *syncp,
|
|
unsigned long flags)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
write_seqcount_end(&syncp->seq);
|
|
local_irq_restore(flags);
|
|
#endif
|
|
}
|
|
|
|
static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
return read_seqcount_begin(&syncp->seq);
|
|
#else
|
|
return 0;
|
|
#endif
|
|
}
|
|
|
|
static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
|
|
preempt_disable();
|
|
#endif
|
|
return __u64_stats_fetch_begin(syncp);
|
|
}
|
|
|
|
static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
|
|
unsigned int start)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
return read_seqcount_retry(&syncp->seq, start);
|
|
#else
|
|
return false;
|
|
#endif
|
|
}
|
|
|
|
static inline bool u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
|
|
unsigned int start)
|
|
{
|
|
#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
|
|
preempt_enable();
|
|
#endif
|
|
return __u64_stats_fetch_retry(syncp, start);
|
|
}
|
|
|
|
/*
|
|
* In case irq handlers can update u64 counters, readers can use following helpers
|
|
* - SMP 32bit arches use seqcount protection, irq safe.
|
|
* - UP 32bit must disable irqs.
|
|
* - 64bit have no problem atomically reading u64 values, irq safe.
|
|
*/
|
|
static inline unsigned int u64_stats_fetch_begin_irq(const struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
|
|
local_irq_disable();
|
|
#endif
|
|
return __u64_stats_fetch_begin(syncp);
|
|
}
|
|
|
|
static inline bool u64_stats_fetch_retry_irq(const struct u64_stats_sync *syncp,
|
|
unsigned int start)
|
|
{
|
|
#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
|
|
local_irq_enable();
|
|
#endif
|
|
return __u64_stats_fetch_retry(syncp, start);
|
|
}
|
|
|
|
#endif /* _LINUX_U64_STATS_SYNC_H */
|