From b6b3ecc71a0664d44ed8d087d583aee98fbf492a Mon Sep 17 00:00:00 2001 From: Eric Dumazet <eric.dumazet@gmail.com> Date: Thu, 24 Jun 2010 00:04:38 +0000 Subject: [PATCH] net: u64_stats_sync improvements - Add a comment about interrupts: 6) If counter might be written by an interrupt, readers should block interrupts. - Fix a typo in sample of use. Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net> --- include/linux/u64_stats_sync.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h index d0505156ed52..b38e3a58de83 100644 --- a/include/linux/u64_stats_sync.h +++ b/include/linux/u64_stats_sync.h @@ -23,6 +23,10 @@ * pure reads. But if they have to fetch many values, it's better to not allow * preemptions/interruptions to avoid many retries. * + * 6) If counter might be written by an interrupt, readers should block interrupts. + * (On UP, there is no seqcount_t protection, a reader allowing interrupts could + * read partial values) + * * Usage : * * Stats producer (writer) should use following template granted it already got @@ -46,7 +50,7 @@ * start = u64_stats_fetch_begin(&stats->syncp); * tbytes = stats->bytes64; // non atomic operation * tpackets = stats->packets64; // non atomic operation - * } while (u64_stats_fetch_retry(&stats->lock, syncp)); + * } while (u64_stats_fetch_retry(&stats->syncp, start)); * * * Example of use in drivers/net/loopback.c, using per_cpu containers, -- GitLab