Nikolay Aleksandrov
2021-Feb-10 11:05 UTC
[Bridge] [PATCH v3 net-next 00/11] Cleanup in brport flags switchdev offload for DSA
On 10/02/2021 13:01, Vladimir Oltean wrote:> On Wed, Feb 10, 2021 at 12:52:33PM +0200, Nikolay Aleksandrov wrote: >> On 10/02/2021 12:45, Vladimir Oltean wrote: >>> Hi Nikolay, >>> >>> On Wed, Feb 10, 2021 at 12:31:43PM +0200, Nikolay Aleksandrov wrote: >>>> Hi Vladimir, >>>> Let's take a step back for a moment and discuss the bridge unlock/lock sequences >>>> that come with this set. I'd really like to avoid those as they're a recipe >>>> for future problems. The only good way to achieve that currently is to keep >>>> the PRE_FLAGS call and do that in unsleepable context but move the FLAGS call >>>> after the flags have been changed (if they have changed obviously). That would >>>> make the code read much easier since we'll have all our lock/unlock sequences >>>> in the same code blocks and won't play games to get sleepable context. >>>> Please let's think and work in that direction, rather than having: >>>> + spin_lock_bh(&p->br->lock); >>>> + if (err) { >>>> + netdev_err(p->dev, "%s\n", extack._msg); >>>> + return err; >>>> } >>>> + >>>> >>>> which immediately looks like a bug even though after some code checking we can >>>> verify it's ok. WDYT? >>>> >>>> I plan to get rid of most of the br->lock since it's been abused for a very long >>>> time because it's essentially STP lock, but people have started using it for other >>>> things and I plan to fix that when I get more time. >>> >>> This won't make the sysfs codepath any nicer, will it? >>> >> >> Currently we'll have to live with a hack that checks if the flags have changed. I agree >> it won't be pretty, but we won't have to unlock and lock again in the middle of the >> called function and we'll have all our locking in the same place, easier to verify and >> later easier to remove. Once I get rid of most of the br->lock usage we can revisit >> the drop of PRE_FLAGS if it's a problem. The alternative is to change the flags, then >> send the switchdev notification outside of the lock and revert the flags if it doesn't >> go through which doesn't sound much better. >> I'm open to any other suggestions, but definitely would like to avoid playing locking games. >> Even if it means casing out flag setting from all other store_ functions for sysfs. > > By casing out flag settings you mean something like this? > > > #define BRPORT_ATTR(_name, _mode, _show, _store) \ > const struct brport_attribute brport_attr_##_name = { \ > .attr = {.name = __stringify(_name), \ > .mode = _mode }, \ > .show = _show, \ > .store_unlocked = _store, \ > }; > > #define BRPORT_ATTR_FLAG(_name, _mask) \ > static ssize_t show_##_name(struct net_bridge_port *p, char *buf) \ > { \ > return sprintf(buf, "%d\n", !!(p->flags & _mask)); \ > } \ > static int store_##_name(struct net_bridge_port *p, unsigned long v) \ > { \ > return store_flag(p, v, _mask); \ > } \ > static BRPORT_ATTR(_name, 0644, \ > show_##_name, store_##_name) > > static ssize_t brport_store(struct kobject *kobj, > struct attribute *attr, > const char *buf, size_t count) > { > ... > > } else if (brport_attr->store_unlocked) { > val = simple_strtoul(buf, &endp, 0); > if (endp == buf) > goto out_unlock; > ret = brport_attr->store_unlocked(p, val); > } >Yes, this can work but will need a bit more changes because of br_port_flags_change(). Then the netlink side can be modeled in a similar way.
Vladimir Oltean
2021-Feb-10 12:01 UTC
[Bridge] [PATCH v3 net-next 00/11] Cleanup in brport flags switchdev offload for DSA
On Wed, Feb 10, 2021 at 01:05:57PM +0200, Nikolay Aleksandrov wrote:> On 10/02/2021 13:01, Vladimir Oltean wrote: > > On Wed, Feb 10, 2021 at 12:52:33PM +0200, Nikolay Aleksandrov wrote: > >> On 10/02/2021 12:45, Vladimir Oltean wrote: > >>> Hi Nikolay, > >>> > >>> On Wed, Feb 10, 2021 at 12:31:43PM +0200, Nikolay Aleksandrov wrote: > >>>> Hi Vladimir, > >>>> Let's take a step back for a moment and discuss the bridge unlock/lock sequences > >>>> that come with this set. I'd really like to avoid those as they're a recipe > >>>> for future problems. The only good way to achieve that currently is to keep > >>>> the PRE_FLAGS call and do that in unsleepable context but move the FLAGS call > >>>> after the flags have been changed (if they have changed obviously). That would > >>>> make the code read much easier since we'll have all our lock/unlock sequences > >>>> in the same code blocks and won't play games to get sleepable context. > >>>> Please let's think and work in that direction, rather than having: > >>>> + spin_lock_bh(&p->br->lock); > >>>> + if (err) { > >>>> + netdev_err(p->dev, "%s\n", extack._msg); > >>>> + return err; > >>>> } > >>>> + > >>>> > >>>> which immediately looks like a bug even though after some code checking we can > >>>> verify it's ok. WDYT? > >>>> > >>>> I plan to get rid of most of the br->lock since it's been abused for a very long > >>>> time because it's essentially STP lock, but people have started using it for other > >>>> things and I plan to fix that when I get more time. > >>> > >>> This won't make the sysfs codepath any nicer, will it? > >>> > >> > >> Currently we'll have to live with a hack that checks if the flags have changed. I agree > >> it won't be pretty, but we won't have to unlock and lock again in the middle of the > >> called function and we'll have all our locking in the same place, easier to verify and > >> later easier to remove. Once I get rid of most of the br->lock usage we can revisit > >> the drop of PRE_FLAGS if it's a problem. The alternative is to change the flags, then > >> send the switchdev notification outside of the lock and revert the flags if it doesn't > >> go through which doesn't sound much better. > >> I'm open to any other suggestions, but definitely would like to avoid playing locking games. > >> Even if it means casing out flag setting from all other store_ functions for sysfs. > > > > By casing out flag settings you mean something like this? > > > > > > #define BRPORT_ATTR(_name, _mode, _show, _store) \ > > const struct brport_attribute brport_attr_##_name = { \ > > .attr = {.name = __stringify(_name), \ > > .mode = _mode }, \ > > .show = _show, \ > > .store_unlocked = _store, \ > > }; > > > > #define BRPORT_ATTR_FLAG(_name, _mask) \ > > static ssize_t show_##_name(struct net_bridge_port *p, char *buf) \ > > { \ > > return sprintf(buf, "%d\n", !!(p->flags & _mask)); \ > > } \ > > static int store_##_name(struct net_bridge_port *p, unsigned long v) \ > > { \ > > return store_flag(p, v, _mask); \ > > } \ > > static BRPORT_ATTR(_name, 0644, \ > > show_##_name, store_##_name) > > > > static ssize_t brport_store(struct kobject *kobj, > > struct attribute *attr, > > const char *buf, size_t count) > > { > > ... > > > > } else if (brport_attr->store_unlocked) { > > val = simple_strtoul(buf, &endp, 0); > > if (endp == buf) > > goto out_unlock; > > ret = brport_attr->store_unlocked(p, val); > > } > > > > Yes, this can work but will need a bit more changes because of br_port_flags_change(). > Then the netlink side can be modeled in a similar way.What I just don't understand is how others can get away with doing sleepable work in atomic context but I can't make the notifier blocking by dropping a spinlock which isn't needed there, because it looks ugly :D