From: Minchan Kim <minchan@kernel.org>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: ngupta@vflare.org, sergey.senozhatsky.work@gmail.com,
axboe@kernel.dk, mbenes@suse.com, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] zram: fix crashes due to use of cpu hotplug multistate
Date: Thu, 11 Mar 2021 18:08:35 -0800 [thread overview]
Message-ID: <YErNI4mv5sK613ed@google.com> (raw)
In-Reply-To: <20210310131115.GQ4332@42.do-not-panic.com>
On Wed, Mar 10, 2021 at 01:11:15PM +0000, Luis Chamberlain wrote:
> On Mon, Mar 08, 2021 at 06:55:30PM -0800, Minchan Kim wrote:
> > On Sat, Mar 06, 2021 at 02:20:34AM +0000, Luis Chamberlain wrote:
> > > The zram driver makes use of cpu hotplug multistate support,
> > > whereby it associates a zram compression stream per CPU. To
> > > support CPU hotplug multistate a callback enabled to allow
> > > the driver to do what it needs when a CPU hotplugs.
> > >
> > > It is however currently possible to end up removing the
> > > zram driver callback prior to removing the zram compression
> > > streams per CPU. This would leave these compression streams
> > > hanging.
> > >
> > > We need to fix ordering for driver load / removal, zram
> > > device additions, in light of the driver's use of cpu
> > > hotplug multistate. Since the zram driver exposes many
> > > sysfs attribute which can also muck with the comrpession
> > > streams this also means we can hit page faults today easily.
> >
> > Hi Luis,
> >
> > First of all, thanks for reporting the ancient bugs.
> >
> > Looks like you found several bugs and I am trying to digest them
> > from your description to understand more clear. I need to ask
> > stupid questions, first.
> >
> > If I understand correctly, bugs you found were related to module
> > unloading race while the zram are still working.
> > If so, couldn't we fix the bug like this(it's not a perfect
> > patch but just wanted to show close module unloading race)?
> > (I might miss other pieces here. Let me know. Thanks!)
> >
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index a711a2e2a794..646ae9e0b710 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -1696,6 +1696,8 @@ static void zram_reset_device(struct zram *zram)
> > return;
> > }
> >
> > + module_put(THIS_MODULE);
> > +
> > comp = zram->comp;
> > disksize = zram->disksize;
> > zram->disksize = 0;
> > @@ -1744,13 +1746,19 @@ static ssize_t disksize_store(struct device *dev,
> > goto out_free_meta;
> > }
> >
> > + if (!try_module_get(THIS_MODULE))
> > + goto out_free_zcomp;
> > +
> > zram->comp = comp;
> > zram->disksize = disksize;
> > +
> > set_capacity_and_notify(zram->disk, zram->disksize >> SECTOR_SHIFT);
> > up_write(&zram->init_lock);
> >
> > return len;
> >
> > +out_free_zcomp:
> > + zcomp_destroy(comp);
> > out_free_meta:
> > zram_meta_free(zram, disksize);
> > out_unlock:
>
> This still allows for a crash on the driver by running the zram02.sh script twice.
>
> Mar 09 14:52:19 kdevops-blktests-block-dev kernel: zram0: detected capacity change from 209715200 to 0
> Mar 09 14:52:19 kdevops-blktests-block-dev kernel: BUG: unable to handle page fault for address: ffffba7db7904008
> Mar 09 14:52:19 kdevops-blktests-block-dev kernel: #PF: supervisor read access in kernel mode
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: #PF: error_code(0x0000) - not-present page
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: PGD 100000067 P4D 100000067 PUD 100311067 PMD 14cd2f067 PTE 0
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: Oops: 0000 [#1] SMP NOPTI
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: CPU: 0 PID: 2137 Comm: zram02.sh Tainted: G E 5.12.0-rc1-next-20210304+ #4
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: RIP: 0010:zram_free_page+0x1b/0xf0 [zram]
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: Code: 1f 44 00 00 48 89 c8 c3 0f 1f 80 00 00 00 00 0f 1f 44 00 00 41 54 49 89 f4 55 89 f5 53 48 8b 17 48 c1 e5 04 48 89 f>
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: RSP:0018:ffffba7d808f3d88 EFLAGS: 00010286
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: RAX: 0000000000000000 RBX: ffff9eee5317d200 RCX: 0000000000000000
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: RDX: ffffba7db7904000 RSI: 0000000000000000 RDI: ffff9eee5317d200
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: RBP: 0000000000000000 R08: 00000008f78bb1d3 R09: 0000000000000000
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: R10: 0000000000000008 R11: 0000000000000000 R12: 0000000000000000
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: R13: ffff9eee53d4cb00 R14: ffff9eee5317d220 R15: ffff9eee70508b80
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: FS: 00007f4bb1482580(0000) GS:ffff9eef77c00000(0000) knlGS:0000000000000000
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: CR2: ffffba7db7904008 CR3: 0000000107e9c000 CR4: 0000000000350ef0
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: Call Trace:
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: zram_reset_device+0xe9/0x150 [zram]
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: reset_store+0x9a/0x100 [zram]
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: kernfs_fop_write_iter+0x124/0x1b0
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: new_sync_write+0x11c/0x1b0
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: vfs_write+0x1c2/0x260
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: ksys_write+0x5f/0xe0
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: do_syscall_64+0x33/0x80
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: entry_SYSCALL_64_after_hwframe+0x44/0xae
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: RIP: 0033:0x7f4bb13aaf33
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: Code: 8b 15 61 ef 0c 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 64 8b 04 25 18 00
> 00 00 85 c0 75 14 b8 01 00 0>
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: RSP: 002b:00007ffce0090d88 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: RAX: ffffffffffffffda RBX: 000055a17c4a14b0 RCX: 00007f4bb13aaf33
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: RDX: 0000000000000002 RSI: 000055a17c4a14b0 RDI: 0000000000000001
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: RBP: 0000000000000002 R08: 000055a17c48a1d0 R09: 0000000000000000
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: R10: 000055a17c48a1d1 R11: 0000000000000246 R12: 0000000000000001
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: R13: 0000000000000002 R14: 7fffffffffffffff R15: 0000000000000000
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: Modules linked in: zram(E) zsmalloc(E) xfs(E) crct10dif_pclmul(E) crc32_pclmul(E) ghash_clmulni_intel(E) joydev(E) evdev(>
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: zram0: detected capacity change from 0 to 209715200
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: CR2: ffffba7db7904008
> Mar 09 14:52:20 kdevops-blktests-block-dev kernel: ---[ end trace 534ee1d0b880dd90 ]---
>
> I can try to modify it to include second patch first, as that is
> required. There are two separate bugs here. Or was your goalt to
> try to address both with only one patch?
I am trying to understand problem first.
next prev parent reply other threads:[~2021-03-12 2:09 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-06 2:20 [PATCH 0/2] zram: fix few ltp zram02.sh crashes Luis Chamberlain
2021-03-06 2:20 ` [PATCH 1/2] zram: fix crashes due to use of cpu hotplug multistate Luis Chamberlain
2021-03-09 2:55 ` Minchan Kim
2021-03-10 13:11 ` Luis Chamberlain
2021-03-10 21:25 ` Luis Chamberlain
2021-03-12 2:08 ` Minchan Kim [this message]
2021-03-10 21:21 ` Luis Chamberlain
2021-03-12 2:14 ` Minchan Kim
2021-03-12 18:32 ` Luis Chamberlain
2021-03-12 19:28 ` Minchan Kim
2021-03-19 19:09 ` Luis Chamberlain
2021-03-22 16:37 ` Minchan Kim
2021-03-22 20:41 ` Luis Chamberlain
2021-03-22 22:12 ` Minchan Kim
2021-04-01 23:59 ` Luis Chamberlain
2021-04-02 7:54 ` Greg KH
2021-04-02 18:30 ` Luis Chamberlain
2021-04-03 6:13 ` Greg KH
[not found] ` <20210406003152.GZ4332@42.do-not-panic.com>
2021-04-06 12:00 ` Miroslav Benes
2021-04-06 15:54 ` Josh Poimboeuf
2021-04-07 14:09 ` Peter Zijlstra
2021-04-07 15:30 ` Josh Poimboeuf
2021-04-07 16:48 ` Peter Zijlstra
2021-04-07 20:17 ` Josh Poimboeuf
2021-04-08 6:18 ` Greg KH
2021-04-08 13:16 ` Steven Rostedt
2021-04-08 13:37 ` Josh Poimboeuf
2021-04-08 1:37 ` Thomas Gleixner
2021-04-08 6:16 ` Greg KH
2021-04-08 8:01 ` Jiri Kosina
2021-04-08 8:09 ` Greg KH
2021-04-08 8:35 ` Jiri Kosina
2021-04-08 8:55 ` Greg KH
2021-04-08 18:40 ` Luis Chamberlain
2021-04-09 3:01 ` Kees Cook
2021-04-05 17:07 ` Minchan Kim
2021-04-05 19:00 ` Luis Chamberlain
2021-04-05 19:58 ` Minchan Kim
2021-04-06 0:29 ` Luis Chamberlain
2021-04-07 1:23 ` Minchan Kim
2021-04-07 1:38 ` Minchan Kim
2021-04-07 14:52 ` Luis Chamberlain
2021-04-07 14:50 ` Luis Chamberlain
2021-03-06 2:20 ` [PATCH 2/2] zram: fix races of sysfs attribute removal and usage Luis Chamberlain
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