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authorJan Stancek <jstancek@redhat.com>2019-07-18 10:51:25 +0200
committerIngo Molnar <mingo@kernel.org>2019-07-25 15:39:23 +0200
commite1b98fa316648420d0434d9ff5b92ad6609ba6c3 (patch)
treea618506f2c00131a3eb9e764ee4422311a2b2f4c /kernel/locking
parent78134300579a45f527ca173ec8fdb4701b69f16e (diff)
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 <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>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/rwsem.c2
1 files changed, 2 insertions, 0 deletions
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);