| Message ID | 20211021095919.bi3szpt3c2kcoiso@linutronix.de (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | c5c6e589a8c811c7f20024cc22209ae984fc2b98 |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next] net: stats: Read the statistics in ___gnet_stats_copy_basic() instead of adding. | expand |
| Context | Check | Description |
|---|---|---|
| netdev/cover_letter | success | Single patches do not need cover letters |
| netdev/fixes_present | success | Fixes tag not required for -next series |
| netdev/patch_count | success | Link |
| netdev/tree_selection | success | Clearly marked for net-next |
| netdev/subject_prefix | success | Link |
| netdev/cc_maintainers | success | CCed 5 of 5 maintainers |
| netdev/source_inline | success | Was 0 now: 0 |
| netdev/verify_signedoff | success | Signed-off-by tag matches author and committer |
| netdev/module_param | success | Was 0 now: 0 |
| netdev/build_32bit | success | Errors and warnings before: 7 this patch: 7 |
| netdev/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| netdev/verify_fixes | success | Fixes tag looks correct |
| netdev/checkpatch | warning | WARNING: line length of 81 exceeds 80 columns |
| netdev/build_allmodconfig_warn | success | Errors and warnings before: 7 this patch: 7 |
| netdev/header_inline | success | No static functions without inline keyword in header files |
Hello: This patch was applied to netdev/net-next.git (master) by David S. Miller <davem@davemloft.net>: On Thu, 21 Oct 2021 11:59:19 +0200 you wrote: > Since the rework, the statistics code always adds up the byte and packet > value(s). On 32bit architectures a seqcount_t is used in > gnet_stats_basic_sync to ensure that the 64bit values are not modified > during the read since two 32bit loads are required. The usage of a > seqcount_t requires a lock to ensure that only one writer is active at a > time. This lock leads to disabled preemption during the update. > > [...] Here is the summary with links: - [net-next] net: stats: Read the statistics in ___gnet_stats_copy_basic() instead of adding. https://git.kernel.org/netdev/net-next/c/c5c6e589a8c8 You are awesome, thank you!
diff --git a/net/core/gen_stats.c b/net/core/gen_stats.c index 15c270e22c5ef..a10335b4ba2d0 100644 --- a/net/core/gen_stats.c +++ b/net/core/gen_stats.c @@ -171,20 +171,51 @@ void gnet_stats_add_basic(struct gnet_stats_basic_sync *bstats, } EXPORT_SYMBOL(gnet_stats_add_basic); +static void gnet_stats_read_basic(u64 *ret_bytes, u64 *ret_packets, + struct gnet_stats_basic_sync __percpu *cpu, + struct gnet_stats_basic_sync *b, bool running) +{ + unsigned int start; + + if (cpu) { + u64 t_bytes = 0, t_packets = 0; + int i; + + for_each_possible_cpu(i) { + struct gnet_stats_basic_sync *bcpu = per_cpu_ptr(cpu, i); + unsigned int start; + u64 bytes, packets; + + do { + start = u64_stats_fetch_begin_irq(&bcpu->syncp); + bytes = u64_stats_read(&bcpu->bytes); + packets = u64_stats_read(&bcpu->packets); + } while (u64_stats_fetch_retry_irq(&bcpu->syncp, start)); + + t_bytes += bytes; + t_packets += packets; + } + *ret_bytes = t_bytes; + *ret_packets = t_packets; + return; + } + do { + if (running) + start = u64_stats_fetch_begin_irq(&b->syncp); + *ret_bytes = u64_stats_read(&b->bytes); + *ret_packets = u64_stats_read(&b->packets); + } while (running && u64_stats_fetch_retry_irq(&b->syncp, start)); +} + static int ___gnet_stats_copy_basic(struct gnet_dump *d, struct gnet_stats_basic_sync __percpu *cpu, struct gnet_stats_basic_sync *b, int type, bool running) { - struct gnet_stats_basic_sync bstats; u64 bstats_bytes, bstats_packets; - gnet_stats_basic_sync_init(&bstats); - gnet_stats_add_basic(&bstats, cpu, b, running); - - bstats_bytes = u64_stats_read(&bstats.bytes); - bstats_packets = u64_stats_read(&bstats.packets); + gnet_stats_read_basic(&bstats_bytes, &bstats_packets, cpu, b, running); if (d->compat_tc_stats && type == TCA_STATS_BASIC) { d->tc_stats.bytes = bstats_bytes;
Since the rework, the statistics code always adds up the byte and packet value(s). On 32bit architectures a seqcount_t is used in gnet_stats_basic_sync to ensure that the 64bit values are not modified during the read since two 32bit loads are required. The usage of a seqcount_t requires a lock to ensure that only one writer is active at a time. This lock leads to disabled preemption during the update. The lack of disabling preemption is now creating a warning as reported by Naresh since the query done by gnet_stats_copy_basic() is in preemptible context. For ___gnet_stats_copy_basic() there is no need to disable preemption since the update is performed on stack and can't be modified by another writer. Instead of disabling preemption, to avoid the warning, simply create a read function to just read the values and return as u64. Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> Fixes: 67c9e6270f301 ("net: sched: Protect Qdisc::bstats with u64_stats") Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- net/core/gen_stats.c | 43 +++++++++++++++++++++++++++++++++++++------ 1 file changed, 37 insertions(+), 6 deletions(-)