Each CPU has SHMEM_INO_BATCH inodes available in `->ino_batch' which is
per-CPU. Access here is serialized by disabling preemption. If the pool
is empty, it gets reloaded from `->next_ino'. Access here is serialized
by ->stat_lock which is a spinlock_t and can not be acquired with disabled
preemption.
One way around it would make per-CPU ino_batch struct containing the inode
number a local_lock_t.
Another solution is to promote ->stat_lock to a raw_spinlock_t. The
critical sections are short. The mpol_put() must be moved outside of the
critical section to avoid invoking the destructor with disabled
preemption.
Link: https://lkml.kernel.org/r/20210806142916.jdwkb5bx62q5fwfo@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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