2020-06-10 16:36:47

by Yue Haibing

Subject: [PATCH] ext4: mballoc: Disable preemption before getting per-CPU pointer

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+ #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: 07b5b8e1ac40 ("ext4: mballoc: introduce pcpu seqcnt for freeing PA to improve ENOSPC handling")
Signed-off-by: YueHaibing <[email protected]>
---
fs/ext4/mballoc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index a9083113a8c0..30b3bfb1e06a 100644
--- 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);
--
2.20.1

2020-06-11 01:24:38

by Ritesh Harjani

Subject: Re: [PATCH] ext4: mballoc: Disable preemption before getting per-CPU pointer

Hello,

Fix for this is already submitted @

https://patchwork.ozlabs.org/project/linux-ext4/patch/534f275016296996f54ecf65168bb3392b6f653d.1591699601.git.riteshh@linux.ibm.com/

-ritesh

On 6/10/20 7:19 PM, YueHaibing wrote:
> 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+ #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: 07b5b8e1ac40 ("ext4: mballoc: introduce pcpu seqcnt for freeing PA to improve ENOSPC handling")
> Signed-off-by: YueHaibing <[email protected]>
> ---
> fs/ext4/mballoc.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index a9083113a8c0..30b3bfb1e06a 100644
> --- 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);
>