netdev - [PATCH V2 bpf-next 3/3] bpf: use u64_stats_t in struct bpf_prog

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Message-Id: <20211026214133.3114279-4-eric.dumazet@gmail.com>
Date:   Tue, 26 Oct 2021 14:41:33 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        bpf <bpf@...r.kernel.org>
Subject: [PATCH V2 bpf-next 3/3] bpf: use u64_stats_t in struct bpf_prog_stats

From: Eric Dumazet <edumazet@...gle.com>

Commit 316580b69d0a ("u64_stats: provide u64_stats_t type")
fixed possible load/store tearing on 64bit arches.

For instance the following C code

stats->nsecs += sched_clock() - start;

Could be rightfully implemented like this by a compiler,
confusing concurrent readers a lot:

stats->nsecs += sched_clock();
// arbitrary delay
stats->nsecs -= start;

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
---
 include/linux/filter.h  | 10 +++++-----
 kernel/bpf/syscall.c    | 18 ++++++++++++------
 kernel/bpf/trampoline.c |  6 +++---
 3 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 2fffe9cc50f946f24f4f78b59902bad91f910e5b..9782e32458522273b314579e62c6215ebb07a617 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -553,9 +553,9 @@ struct bpf_binary_header {
 };
 
 struct bpf_prog_stats {
-	u64 cnt;
-	u64 nsecs;
-	u64 misses;
+	u64_stats_t cnt;
+	u64_stats_t nsecs;
+	u64_stats_t misses;
 	struct u64_stats_sync syncp;
 } __aligned(2 * sizeof(u64));
 
@@ -617,8 +617,8 @@ static __always_inline u32 __bpf_prog_run(const struct bpf_prog *prog,
 		ret = dfunc(ctx, prog->insnsi, prog->bpf_func);
 		stats = this_cpu_ptr(prog->stats);
 		flags = u64_stats_update_begin_irqsave(&stats->syncp);
-		stats->cnt++;
-		stats->nsecs += sched_clock() - start;
+		u64_stats_inc(&stats->cnt);
+		u64_stats_add(&stats->nsecs, sched_clock() - start);
 		u64_stats_update_end_irqrestore(&stats->syncp, flags);
 	} else {
 		ret = dfunc(ctx, prog->insnsi, prog->bpf_func);
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 4e50c0bfdb7d38e1c929a499c0688f59b9caf618..7a147c6eb30b2b771539cce642a359bd4dec66f8 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1804,8 +1804,14 @@ static int bpf_prog_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+struct bpf_prog_kstats {
+	u64 nsecs;
+	u64 cnt;
+	u64 misses;
+};
+
 static void bpf_prog_get_stats(const struct bpf_prog *prog,
-			       struct bpf_prog_stats *stats)
+			       struct bpf_prog_kstats *stats)
 {
 	u64 nsecs = 0, cnt = 0, misses = 0;
 	int cpu;
@@ -1818,9 +1824,9 @@ static void bpf_prog_get_stats(const struct bpf_prog *prog,
 		st = per_cpu_ptr(prog->stats, cpu);
 		do {
 			start = u64_stats_fetch_begin_irq(&st->syncp);
-			tnsecs = st->nsecs;
-			tcnt = st->cnt;
-			tmisses = st->misses;
+			tnsecs = u64_stats_read(&st->nsecs);
+			tcnt = u64_stats_read(&st->cnt);
+			tmisses = u64_stats_read(&st->misses);
 		} while (u64_stats_fetch_retry_irq(&st->syncp, start));
 		nsecs += tnsecs;
 		cnt += tcnt;
@@ -1836,7 +1842,7 @@ static void bpf_prog_show_fdinfo(struct seq_file *m, struct file *filp)
 {
 	const struct bpf_prog *prog = filp->private_data;
 	char prog_tag[sizeof(prog->tag) * 2 + 1] = { };
-	struct bpf_prog_stats stats;
+	struct bpf_prog_kstats stats;
 
 	bpf_prog_get_stats(prog, &stats);
 	bin2hex(prog_tag, prog->tag, sizeof(prog->tag));
@@ -3575,7 +3581,7 @@ static int bpf_prog_get_info_by_fd(struct file *file,
 	struct bpf_prog_info __user *uinfo = u64_to_user_ptr(attr->info.info);
 	struct bpf_prog_info info;
 	u32 info_len = attr->info.info_len;
-	struct bpf_prog_stats stats;
+	struct bpf_prog_kstats stats;
 	char __user *uinsns;
 	u32 ulen;
 	int err;
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index e5963de368ed34874414d097bc6614ff7e168dd3..e98de5e73ba59f756480cc5f962849be1859751b 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -545,7 +545,7 @@ static void notrace inc_misses_counter(struct bpf_prog *prog)
 
 	stats = this_cpu_ptr(prog->stats);
 	u64_stats_update_begin(&stats->syncp);
-	stats->misses++;
+	u64_stats_inc(&stats->misses);
 	u64_stats_update_end(&stats->syncp);
 }
 
@@ -590,8 +590,8 @@ static void notrace update_prog_stats(struct bpf_prog *prog,
 
 		stats = this_cpu_ptr(prog->stats);
 		flags = u64_stats_update_begin_irqsave(&stats->syncp);
-		stats->cnt++;
-		stats->nsecs += sched_clock() - start;
+		u64_stats_inc(&stats->cnt);
+		u64_stats_add(&stats->nsecs, sched_clock() - start);
 		u64_stats_update_end_irqrestore(&stats->syncp, flags);
 	}
 }
-- 
2.33.0.1079.g6e70778dc9-goog