[syzbot] [erofs?] BUG: using smp_processor_id() in preemptible code in z_erofs_get_gbuf

[Edward Adam Davis]

please test wrong context using smp_processor_id

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 2b3d5988ae2c

diff --git a/fs/erofs/zutil.c b/fs/erofs/zutil.c
index 9687cad8be96..0a3d9eecbf16 100644
--- a/fs/erofs/zutil.c
+++ b/fs/erofs/zutil.c
@@ -35,8 +35,11 @@ void *z_erofs_get_gbuf(unsigned int requiredpages)
 	__acquires(gbuf->lock)
 {
 	struct z_erofs_gbuf *gbuf;
+	unsigned long flags;
 
+	local_irq_save(flags);
 	gbuf = &z_erofs_gbufpool[z_erofs_gbuf_id()];
+	local_irq_restore(flags);
 	spin_lock(&gbuf->lock);
 	/* check if the buffer is too small */
 	if (requiredpages > gbuf->nrpages) {