Commit-ID: e1b98fa316648420d0434d9ff5b92ad6609ba6c3
Gitweb: https://git.kernel.org/tip/e1b98fa316648420d0434d9ff5b92ad6609ba6c3
Author: Jan Stancek <jstan...@redhat.com>
AuthorDate: Thu, 18 Jul 2019 10:51:25 +0200
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Thu, 25 Jul 2019 15:39:23 +0200
locking/rwsem: Add missing ACQUIRE to read_slowpath exit when queue is empty
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 <jstan...@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Reviewed-by: Will Deacon <w...@kernel.org>
Acked-by: Waiman Long <long...@redhat.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: dbu...@suse.de
Fixes: 4b486b535c33 ("locking/rwsem: Exit read lock slowpath if queue empty &
no writer")
Link:
https://lkml.kernel.org/r/50b8914e20d1d62bb2dee42d342836c2c16ebee7.1563438048.git.jstan...@redhat.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
kernel/locking/rwsem.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index bc91aacaab58..d3ce7c6c42a6 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1036,6 +1036,8 @@ queue:
*/
if (adjustment && !(atomic_long_read(&sem->count) &
(RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
+ /* Provide lock ACQUIRE */
+ smp_acquire__after_ctrl_dep();
raw_spin_unlock_irq(&sem->wait_lock);
rwsem_set_reader_owned(sem);
lockevent_inc(rwsem_rlock_fast);
