Messages in this thread | | | Date | Tue, 27 Aug 2019 10:11:39 -0400 (EDT) | From | Jan Stancek <> | Subject | Re: [PATCH v5.2 1/2] locking/rwsem: Add missing ACQUIRE to read_slowpath exit when queue is empty |
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----- Original Message ----- > From: Jan Stancek <jstancek@redhat.com> > > [ Upstream commit e1b98fa316648420d0434d9ff5b92ad6609ba6c3 ] > > LTP mtest06 has been observed to occasionally hit "still mapped when > deleted" and following BUG_ON on arm64. > > The extra mapcount originated from pagefault handler, which handled > pagefault for vma that has already been detached. vma is detached > under mmap_sem write lock by detach_vmas_to_be_unmapped(), which > also invalidates vmacache. > > When the pagefault handler (under mmap_sem read lock) calls > find_vma(), vmacache_valid() wrongly reports vmacache as valid. > > After rwsem down_read() returns via 'queue empty' path (as of v5.2), > it does so without an ACQUIRE on sem->count: > > down_read() > __down_read() > rwsem_down_read_failed() > __rwsem_down_read_failed_common() > raw_spin_lock_irq(&sem->wait_lock); > if (list_empty(&sem->wait_list)) { > if (atomic_long_read(&sem->count) >= 0) { > raw_spin_unlock_irq(&sem->wait_lock); > return sem; > > The problem can be reproduced by running LTP mtest06 in a loop and > building the kernel (-j $NCPUS) in parallel. It does reproduces since > v4.20 on arm64 HPE Apollo 70 (224 CPUs, 256GB RAM, 2 nodes). It > triggers reliably in about an hour. > > The patched kernel ran fine for 10+ hours. > > Signed-off-by: Jan Stancek <jstancek@redhat.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Reviewed-by: Will Deacon <will@kernel.org> > Acked-by: Waiman Long <longman@redhat.com> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: dbueso@suse.de > Fixes: 4b486b535c33 ("locking/rwsem: Exit read lock slowpath if queue empty & > no writer") > Link: > https://lkml.kernel.org/r/50b8914e20d1d62bb2dee42d342836c2c16ebee7.1563438048.git.jstancek@redhat.com > Signed-off-by: Ingo Molnar <mingo@kernel.org> > Signed-off-by: Sasha Levin <sashal@kernel.org> > --- > > This is a backport for the v5.2 stable tree. There were multiple reports > of this issue being hit. > > Given that there were a few changes to the code around this, I'd > appreciate an ack before pulling it in.
ACK, both look good to me. I also re-ran reproducer with this series applied on top of 5.2.10, it PASS-ed.
Thanks, Jan
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