ext4: mballoc: Disable preemption before getting per-CPU pointer

YueHaibing · intel-lab-lkp · commit 0f3846e96ddb · 2020-06-10T21:55:14.000+08:00
BUG: using smp_processor_id() in preemptible [00000000] code: kworker/u16:3/2181 caller is ext4_mb_new_blocks+0x388/0xed0 CPU: 2 PID: 2181 Comm: kworker/u16:3 Not tainted 5.7.0+ torvalds#182 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Workqueue: writeback wb_workfn (flush-8:0) Call Trace: dump_stack+0xb9/0xfc debug_smp_processor_id+0xc8/0xd0 ext4_mb_new_blocks+0x388/0xed0 ext4_ext_map_blocks+0xa92/0xff0 ext4_map_blocks+0x34e/0x580 ext4_writepages+0xa28/0x11b0 do_writepages+0x46/0xe0 __writeback_single_inode+0x5f/0x6b0 writeback_sb_inodes+0x290/0x620 __writeback_inodes_wb+0x62/0xb0 wb_writeback+0x36c/0x520 wb_workfn+0x319/0x680 process_one_work+0x271/0x640 worker_thread+0x3a/0x3a0 kthread+0x14e/0x170 ret_from_fork+0x27/0x40 Disable preemption before accessing discard_pa_seq. Fixes: 07b5b8e ("ext4: mballoc: introduce pcpu seqcnt for freeing PA to improve ENOSPC handling") Signed-off-by: YueHaibing <yuehaibing@huawei.com>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
@@ -4708,7 +4708,8 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
 	}
 
 	ac->ac_op = EXT4_MB_HISTORY_PREALLOC;
-	seq = *this_cpu_ptr(&discard_pa_seq);
+	seq = *get_cpu_ptr(&discard_pa_seq);
+	put_cpu_ptr(&discard_pa_seq);
 	if (!ext4_mb_use_preallocated(ac)) {
 		ac->ac_op = EXT4_MB_HISTORY_ALLOC;
 		ext4_mb_normalize_request(ac, ar);

Original file line number	Diff line number	Diff line change
`@@ -4708,7 +4708,8 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,`
`4708`	`4708`	`}`
`4709`	`4709`
`4710`	`4710`	`ac->ac_op = EXT4_MB_HISTORY_PREALLOC;`
`4711`		`- seq = *this_cpu_ptr(&discard_pa_seq);`
	`4711`	`+ seq = *get_cpu_ptr(&discard_pa_seq);`
	`4712`	`+ put_cpu_ptr(&discard_pa_seq);`
`4712`	`4713`	`if (!ext4_mb_use_preallocated(ac)) {`
`4713`	`4714`	`ac->ac_op = EXT4_MB_HISTORY_ALLOC;`
`4714`	`4715`	`ext4_mb_normalize_request(ac, ar);`