Hi Andrew, On Wed, 30 Oct 2013 18:32:41 +0000 (GMT) Jason Baron <jbaron@xxxxxxxxxx> wrote: > > By removing the 'int on_list' field from 'struct epitem', we avoid hitting the > BUILD_BUG_ON() for 'struct epitem' being larger than 128 bytes. > > In file included from include/linux/init.h:4:0, > from fs/eventpoll.c:14: > fs/eventpoll.c: In function 'eventpoll_init': > include/linux/compiler.h:321:20: error: call to '__compiletime_assert_2137' declared with attribute error: BUILD_BUG_ON failed: sizeof(void *) <= 8 && sizeof(struct epitem) > 128 > prefix ## suffix(); \ > > The check to make sure that the 'struct epitem' was actually linked via > epi->fllink was added to avoid having the list removal primitives called twice > for the same 'struct epitem'. However, the double call possibility was removed > by 'Subject: epoll: optimize EPOLL_CTL_DEL using rcu'. There, the call to > 'list_del_init()' in eventpoll_release_file() was removed (we now rely on the > list delete happening entirely in 'ep_remove()', which is called from > eventpoll_release_file()). > > There is also the question as to whether multiple ep_remove() calls could > happen concurrently. This can not happen since EPOLL_CTL_DEL can't > race with eventpoll_release_file() or ep_free() - it has to do an fget() > to proceed. Further, eventpoll_release_file() can not race with ep_free(), > since they both acquire the 'epmutex'. > > Signed-off-by: Jason Baron <jbaron@xxxxxxxxxx> Do you want me to put this in my copy of the mmotm instead of reverting these three? epoll-do-not-take-global-epmutex-for-simple-topologies-fix epoll: do not take global 'epmutex' for simple topologies epoll: optimize EPOLL_CTL_DEL using rcu -- Cheers, Stephen Rothwell sfr@xxxxxxxxxxxxxxxx
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