diff mbox series

[v4,net-next,04/18] net: sysfs: don't hold dev_base_lock while retrieving device statistics

Message ID 20210108002005.3429956-5-olteanv@gmail.com (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series Make .ndo_get_stats64 sleepable | expand

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Context Check Description
netdev/cover_letter success Link
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netdev/patch_count fail Series longer than 15 patches
netdev/tree_selection success Clearly marked for net-next
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netdev/cc_maintainers warning 6 maintainers not CCed: alexanderduyck@fb.com tobias@waldekranz.com wangxiongfeng2@huawei.com christian.brauner@ubuntu.com atenart@kernel.org vladimir.oltean@nxp.com
netdev/source_inline success Was 0 now: 0
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netdev/module_param success Was 0 now: 0
netdev/build_32bit success Errors and warnings before: 1 this patch: 1
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netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 15 lines checked
netdev/build_allmodconfig_warn success Errors and warnings before: 1 this patch: 1
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netdev/stable success Stable not CCed

Commit Message

Vladimir Oltean Jan. 8, 2021, 12:19 a.m. UTC 
From: Vladimir Oltean <vladimir.oltean@nxp.com>

In the effort of making .ndo_get_stats64 be able to sleep, we need to
ensure the callers of dev_get_stats do not use atomic context.

I need to preface this by saying that I have no idea why netstat_show
takes the dev_base_lock rwlock. Two things can be observed:
(a) it does not appear to be due to dev_isalive requiring it for some
    reason, because broadcast_show() also calls dev_isalive() and has
    had no problem existing since the beginning of git.
(b) the dev_get_stats function definitely does not need dev_base_lock
    protection either. In fact, holding the dev_base_lock is the entire
    problem here, because we want to make dev_get_stats sleepable, and
    holding a rwlock gives us atomic context.

So since no protection seems to be necessary, just run unlocked while
retrieving the /sys/class/net/eth0/statistics/* values.

Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
Changes in v4:
None.

Changes in v3:
None.

Changes in v2:
None.

 net/core/net-sysfs.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index daf502c13d6d..8604183678fc 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -585,14 +585,13 @@  static ssize_t netstat_show(const struct device *d,
 	WARN_ON(offset > sizeof(struct rtnl_link_stats64) ||
 		offset % sizeof(u64) != 0);
 
-	read_lock(&dev_base_lock);
 	if (dev_isalive(dev)) {
 		struct rtnl_link_stats64 temp;
 		const struct rtnl_link_stats64 *stats = dev_get_stats(dev, &temp);
 
 		ret = sprintf(buf, fmt_u64, *(u64 *)(((u8 *)stats) + offset));
 	}
-	read_unlock(&dev_base_lock);
+
 	return ret;
 }