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net: fix sk_memory_allocated_{add|sub} vs softirqs 

Jonathan Heathcote reported a regression caused by blamed commit
on aarch64 architecture.

x86 happens to have irq-safe __this_cpu_add_return()
and __this_cpu_sub(), but this is not generic.

I think my confusion came from "struct sock" argument,
because these helpers are called with a locked socket.
But the memory accounting is per-proto (and per-cpu after
the blamed commit). We might cleanup these helpers later
to directly accept a "struct proto *proto" argument.

Switch to this_cpu_add_return() and this_cpu_xchg()
operations, and get rid of preempt_disable()/preempt_enable() pairs.

Fast path becomes a bit faster as a result :)

Many thanks to Jonathan Heathcote for his awesome report and
investigations.

Fixes: 3cd3399dd7 ("net: implement per-cpu reserves for memory_allocated")
Reported-by: Jonathan Heathcote <jonathan.heathcote@bbc.co.uk>
Closes: https://lore.kernel.org/netdev/VI1PR01MB42407D7947B2EA448F1E04EFD10D2@VI1PR01MB4240.eurprd01.prod.exchangelabs.com/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Link: https://lore.kernel.org/r/20240421175248.1692552-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2024-04-21 17:52:48 +00:00 committed by Jakub Kicinski
parent a44f2eb106
commit 3584718cf2
1 changed files with 21 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
include/net/sock.h
View File

@ -1410,32 +1410,34 @@ sk_memory_allocated(const struct sock *sk)
#define SK_MEMORY_PCPU_RESERVE (1 << (20 - PAGE_SHIFT))
extern int sysctl_mem_pcpu_rsv;
static inline void
sk_memory_allocated_add(struct sock *sk, int amt)
static inline void proto_memory_pcpu_drain(struct proto *proto)
{
int local_reserve;
int val = this_cpu_xchg(*proto->per_cpu_fw_alloc, 0);
preempt_disable();
local_reserve = __this_cpu_add_return(*sk->sk_prot->per_cpu_fw_alloc, amt);
if (local_reserve >= READ_ONCE(sysctl_mem_pcpu_rsv)) {
__this_cpu_sub(*sk->sk_prot->per_cpu_fw_alloc, local_reserve);
atomic_long_add(local_reserve, sk->sk_prot->memory_allocated);
}
preempt_enable();
if (val)
atomic_long_add(val, proto->memory_allocated);
}
static inline void
sk_memory_allocated_sub(struct sock *sk, int amt)
sk_memory_allocated_add(const struct sock *sk, int val)
{
int local_reserve;
struct proto *proto = sk->sk_prot;
preempt_disable();
local_reserve = __this_cpu_sub_return(*sk->sk_prot->per_cpu_fw_alloc, amt);
if (local_reserve <= -READ_ONCE(sysctl_mem_pcpu_rsv)) {
__this_cpu_sub(*sk->sk_prot->per_cpu_fw_alloc, local_reserve);
atomic_long_add(local_reserve, sk->sk_prot->memory_allocated);
}
preempt_enable();
val = this_cpu_add_return(*proto->per_cpu_fw_alloc, val);
if (unlikely(val >= READ_ONCE(sysctl_mem_pcpu_rsv)))
proto_memory_pcpu_drain(proto);
}
static inline void
sk_memory_allocated_sub(const struct sock *sk, int val)
{
struct proto *proto = sk->sk_prot;
val = this_cpu_sub_return(*proto->per_cpu_fw_alloc, val);
if (unlikely(val <= -READ_ONCE(sysctl_mem_pcpu_rsv)))
proto_memory_pcpu_drain(proto);
}
#define SK_ALLOC_PERCPU_COUNTER_BATCH 16