Messages in this thread Patch in this message | | | Date | Mon, 17 Nov 2014 23:43:14 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: frequent lockups in 3.18rc4 |
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On Mon, 17 Nov 2014, Thomas Gleixner wrote: > On Mon, 17 Nov 2014, Linus Torvalds wrote: > > llist_for_each_entry_safe(csd, csd_next, entry, llist) { > > - csd->func(csd->info); > > + smp_call_func_t func = csd->func; > > + void *info = csd->info; > > csd_unlock(csd); > > + > > + func(info); > > No, that won't work for synchronous calls: > > CPU 0 CPU 1 > > csd_lock(csd); > queue_csd(); > ipi(); > func = csd->func; > info = csd->info; > csd_unlock(csd); > csd_lock_wait(); > func(info); > > The csd_lock_wait() side will succeed and therefor assume that the > call has been completed while the function has not been called at > all. Interesting explosions to follow. > > The proper solution is to revert that commit and properly analyze the > problem which Jens was trying to solve and work from there.
So a combo of both (Jens and yours) might do the trick. Patch below.
I think what Jens was trying to solve is:
CPU 0 CPU 1
csd_lock(csd); queue_csd(); ipi(); csd->func(csd->info); wait_for_completion(csd); complete(csd); reuse_csd(csd); csd_unlock(csd);
Thanks,
tglx
Index: linux/kernel/smp.c =================================================================== --- linux.orig/kernel/smp.c +++ linux/kernel/smp.c @@ -126,7 +126,7 @@ static void csd_lock(struct call_single_ static void csd_unlock(struct call_single_data *csd) { - WARN_ON((csd->flags & CSD_FLAG_WAIT) && !(csd->flags & CSD_FLAG_LOCK)); + WARN_ON(!(csd->flags & CSD_FLAG_LOCK)); /* * ensure we're all done before releasing data: @@ -250,8 +250,23 @@ static void flush_smp_call_function_queu } llist_for_each_entry_safe(csd, csd_next, entry, llist) { - csd->func(csd->info); - csd_unlock(csd); + + /* + * For synchronous calls we are not allowed to unlock + * before the callback returned. For the async case + * its the responsibility of the caller to keep + * csd->info consistent while the callback runs. + */ + if (csd->flags & CSD_FLAG_WAIT) { + csd->func(csd->info); + csd_unlock(csd); + } else { + smp_call_func_t func = csd->func; + void *info = csd->info; + + csd_unlock(csd); + func(info); + } } /*
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