On 04/19/2019 11:00 AM, Waiman Long wrote: > On 04/19/2019 08:49 AM, Ingo Molnar wrote: >> * Ingo Molnar <mi...@kernel.org> wrote: >> >>> * Waiman Long <long...@redhat.com> wrote: >>> >>>> On 04/18/2019 07:46 PM, Waiman Long wrote: >>>>> v5: >>>>> - Drop v4 patch 1 as it is merged into tip's locking/core branch. >>>>> - Integrate the 2 followup patches into the series. The first >>>>> follow-up patch is broken into 2 pieces. The first piece comes in >>>>> before the "Enable readers spinning on writer" and the 2nd piece >>>>> is merged into the "Enable time-based spinning on reader-owned >>>>> rwsem" patch. The 2nd followup patch is added after that. >>>>> - Add a new patch to make all wake_up_q() calls after dropping >>>>> wait_lock as suggested by PeterZ. >>>>> - Incorporate numerouos suggestions by PeterZ and Davidlohr. >>>> This patchset is still being reviewed by Peter . The purpose of this >>>> series is mainly to sync up the version that Peter has and the ones that >>>> I am working on incorporating his feedback. Further changes may still be >>>> needed. >>>> >>>> I run an overall performance test on this new patchset and present the >>>> data in this cover letter. However, I haven't run performance tests for >>>> individual patches. So the performance data listed in some of the >>>> patches may be stale. >>> Just for those who'd like to follow the scope of changes, find below the >>> v4->v5 interdiff. v5 is now included in tip:WIP.locking/core, and also >>> merged into tip:master. (But not propagated towards linux-next yet.) >> Hm, I'm experiencing early boot hangs with v5, on defconfig-ish x86-64 >> kernels: >> >> [ 0.153940] rcu: Hierarchical RCU implementation. >> [ 0.154289] rcu: RCU restricting CPUs from NR_CPUS=128 to nr_cpu_ids=17. >> [ 0.154829] rcu: RCU calculated value of scheduler-enlistment delay is >> 100 jiffies. >> [ 0.155390] rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=17 >> >> >> I bisected it back to the v5 version of this patch: >> >> 2fd5f60fa4c3: locking/rwsem: Merge owner into count on x86-64 >> >> I'm moving -tip back to -v4 meanwhile. >> >> Thanks, >> >> Ingo > Sorry about that. Will look into that problem. > > -Longman > Yes, there is a bug in that patch. The following change should fix it:
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 19d8fbd50d17..857dff330f9b 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -198,9 +198,15 @@ /* * Task structure pointer compression (64-bit only): * (owner - PAGE_OFFSET) >> (L1_CACHE_SHIFT - 2) + * + * However, init_task may lie outside of the linearly mapped physical + * to virtual memory range and so has to be handled separately. */ static inline unsigned long rwsem_owner_count(struct task_struct *owner) { + if (unlikely(owner == &init_task)) + return RWSEM_WRITER_MASK; + return ((unsigned long)owner - PAGE_OFFSET) >> (L1_CACHE_SHIFT - 2); } @@ -208,6 +214,9 @@ static inline unsigned long rwsem_count_owner(long count) { unsigned long writer = (unsigned long)count & RWSEM_WRITER_MASK; + if (unlikely(writer == RWSEM_WRITER_MASK)) + return (unsigned long)&init_task; + return writer ? (writer << (L1_CACHE_SHIFT - 2)) + PAGE_OFFSET : 0; }