Date:   Thu, 28 Jan 2021 18:16:55 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Hillf Danton <hdanton@...a.com>, netdev <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        syzbot <syzbot+e74a6857f2d0efe3ad81@...kaller.appspotmail.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Simon Horman <simon.horman@...ronome.com>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH] netdevsim: init u64 stats for 32bit hardware

On Thu, Jan 28, 2021 at 5:01 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
>
> On 1/28/21 8:23 AM, Dmitry Vyukov wrote:
> > On Thu, Jan 28, 2021 at 3:43 AM Hillf Danton <hdanton@...a.com> wrote:
> >>
> >> Init the u64 stats in order to avoid the lockdep prints on the 32bit
> >> hardware like
> >
> > FTR this is not just to avoid lockdep prints, but also to prevent very
> > real stalls in production.
>
> Are you sure ?
>
> > u64_stats_init initializes seqlock, if the uninitialized
> > selock->sequence would be odd, the kernel will stall.
>
> Normally the whole netdev structure is zeroed when allocated,
> this is done in alloc_netdev_mqs()
>
> p = kvzalloc(alloc_size, GFP_KERNEL | __GFP_RETRY_MAYFAIL);
>
> So unless kvzalloc() has been changed recently to inject random data
> instead of 0, this bug is really about lockdep only.

You are right, I missed that the object is zero-initialized. Then it's
only a latent bug (if e.g. seqcount_init initializes count to an odd
value).

> > Maintainers, please send this upstream on your earliest convenience,
> > this breaks all 32-bit arches for testing purposes.
> >
> > Thanks
> >
> >>  INFO: trying to register non-static key.
> >>  the code is fine but needs lockdep annotation.
> >>  turning off the locking correctness validator.
> >>  CPU: 0 PID: 4695 Comm: syz-executor.0 Not tainted 5.11.0-rc5-syzkaller #0
> >>  Hardware name: ARM-Versatile Express
> >>  Backtrace:
> >>  [<826fc5b8>] (dump_backtrace) from [<826fc82c>] (show_stack+0x18/0x1c arch/arm/kernel/traps.c:252)
> >>  [<826fc814>] (show_stack) from [<8270d1f8>] (__dump_stack lib/dump_stack.c:79 [inline])
> >>  [<826fc814>] (show_stack) from [<8270d1f8>] (dump_stack+0xa8/0xc8 lib/dump_stack.c:120)
> >>  [<8270d150>] (dump_stack) from [<802bf9c0>] (assign_lock_key kernel/locking/lockdep.c:935 [inline])
> >>  [<8270d150>] (dump_stack) from [<802bf9c0>] (register_lock_class+0xabc/0xb68 kernel/locking/lockdep.c:1247)
> >>  [<802bef04>] (register_lock_class) from [<802baa2c>] (__lock_acquire+0x84/0x32d4 kernel/locking/lockdep.c:4711)
> >>  [<802ba9a8>] (__lock_acquire) from [<802be840>] (lock_acquire.part.0+0xf0/0x554 kernel/locking/lockdep.c:5442)
> >>  [<802be750>] (lock_acquire.part.0) from [<802bed10>] (lock_acquire+0x6c/0x74 kernel/locking/lockdep.c:5415)
> >>  [<802beca4>] (lock_acquire) from [<81560548>] (seqcount_lockdep_reader_access include/linux/seqlock.h:103 [inline])
> >>  [<802beca4>] (lock_acquire) from [<81560548>] (__u64_stats_fetch_begin include/linux/u64_stats_sync.h:164 [inline])
> >>  [<802beca4>] (lock_acquire) from [<81560548>] (u64_stats_fetch_begin include/linux/u64_stats_sync.h:175 [inline])
> >>  [<802beca4>] (lock_acquire) from [<81560548>] (nsim_get_stats64+0xdc/0xf0 drivers/net/netdevsim/netdev.c:70)
> >>  [<8156046c>] (nsim_get_stats64) from [<81e2efa0>] (dev_get_stats+0x44/0xd0 net/core/dev.c:10405)
> >>  [<81e2ef5c>] (dev_get_stats) from [<81e53204>] (rtnl_fill_stats+0x38/0x120 net/core/rtnetlink.c:1211)
> >>  [<81e531cc>] (rtnl_fill_stats) from [<81e59d58>] (rtnl_fill_ifinfo+0x6d4/0x148c net/core/rtnetlink.c:1783)
> >>  [<81e59684>] (rtnl_fill_ifinfo) from [<81e5ceb4>] (rtmsg_ifinfo_build_skb+0x9c/0x108 net/core/rtnetlink.c:3798)
> >>  [<81e5ce18>] (rtmsg_ifinfo_build_skb) from [<81e5d0ac>] (rtmsg_ifinfo_event net/core/rtnetlink.c:3830 [inline])
> >>  [<81e5ce18>] (rtmsg_ifinfo_build_skb) from [<81e5d0ac>] (rtmsg_ifinfo_event net/core/rtnetlink.c:3821 [inline])
> >>  [<81e5ce18>] (rtmsg_ifinfo_build_skb) from [<81e5d0ac>] (rtmsg_ifinfo+0x44/0x70 net/core/rtnetlink.c:3839)
> >>  [<81e5d068>] (rtmsg_ifinfo) from [<81e45c2c>] (register_netdevice+0x664/0x68c net/core/dev.c:10103)
> >>  [<81e455c8>] (register_netdevice) from [<815608bc>] (nsim_create+0xf8/0x124 drivers/net/netdevsim/netdev.c:317)
> >>  [<815607c4>] (nsim_create) from [<81561184>] (__nsim_dev_port_add+0x108/0x188 drivers/net/netdevsim/dev.c:941)
> >>  [<8156107c>] (__nsim_dev_port_add) from [<815620d8>] (nsim_dev_port_add_all drivers/net/netdevsim/dev.c:990 [inline])
> >>  [<8156107c>] (__nsim_dev_port_add) from [<815620d8>] (nsim_dev_probe+0x5cc/0x750 drivers/net/netdevsim/dev.c:1119)
> >>  [<81561b0c>] (nsim_dev_probe) from [<815661dc>] (nsim_bus_probe+0x10/0x14 drivers/net/netdevsim/bus.c:287)
> >>  [<815661cc>] (nsim_bus_probe) from [<811724c0>] (really_probe+0x100/0x50c drivers/base/dd.c:554)
> >>  [<811723c0>] (really_probe) from [<811729c4>] (driver_probe_device+0xf8/0x1c8 drivers/base/dd.c:740)
> >>  [<811728cc>] (driver_probe_device) from [<81172fe4>] (__device_attach_driver+0x8c/0xf0 drivers/base/dd.c:846)
> >>  [<81172f58>] (__device_attach_driver) from [<8116fee0>] (bus_for_each_drv+0x88/0xd8 drivers/base/bus.c:431)
> >>  [<8116fe58>] (bus_for_each_drv) from [<81172c6c>] (__device_attach+0xdc/0x1d0 drivers/base/dd.c:914)
> >>  [<81172b90>] (__device_attach) from [<8117305c>] (device_initial_probe+0x14/0x18 drivers/base/dd.c:961)
> >>  [<81173048>] (device_initial_probe) from [<81171358>] (bus_probe_device+0x90/0x98 drivers/base/bus.c:491)
> >>  [<811712c8>] (bus_probe_device) from [<8116e77c>] (device_add+0x320/0x824 drivers/base/core.c:3109)
> >>  [<8116e45c>] (device_add) from [<8116ec9c>] (device_register+0x1c/0x20 drivers/base/core.c:3182)
> >>  [<8116ec80>] (device_register) from [<81566710>] (nsim_bus_dev_new drivers/net/netdevsim/bus.c:336 [inline])
> >>  [<8116ec80>] (device_register) from [<81566710>] (new_device_store+0x178/0x208 drivers/net/netdevsim/bus.c:215)
> >>  [<81566598>] (new_device_store) from [<8116fcb4>] (bus_attr_store+0x2c/0x38 drivers/base/bus.c:122)
> >>  [<8116fc88>] (bus_attr_store) from [<805b4b8c>] (sysfs_kf_write+0x48/0x54 fs/sysfs/file.c:139)
> >>  [<805b4b44>] (sysfs_kf_write) from [<805b3c90>] (kernfs_fop_write_iter+0x128/0x1ec fs/kernfs/file.c:296)
> >>  [<805b3b68>] (kernfs_fop_write_iter) from [<804d22fc>] (call_write_iter include/linux/fs.h:1901 [inline])
> >>  [<805b3b68>] (kernfs_fop_write_iter) from [<804d22fc>] (new_sync_write fs/read_write.c:518 [inline])
> >>  [<805b3b68>] (kernfs_fop_write_iter) from [<804d22fc>] (vfs_write+0x3dc/0x57c fs/read_write.c:605)
> >>  [<804d1f20>] (vfs_write) from [<804d2604>] (ksys_write+0x68/0xec fs/read_write.c:658)
> >>  [<804d259c>] (ksys_write) from [<804d2698>] (__do_sys_write fs/read_write.c:670 [inline])
> >>  [<804d259c>] (ksys_write) from [<804d2698>] (sys_write+0x10/0x14 fs/read_write.c:667)
> >>  [<804d2688>] (sys_write) from [<80200060>] (ret_fast_syscall+0x0/0x2c arch/arm/mm/proc-v7.S:64)
> >>
> >> Fixes: 83c9e13aa39a ("netdevsim: add software driver for testing offloads")
> >> Reported-by: syzbot+e74a6857f2d0efe3ad81@...kaller.appspotmail.com
> >> Tested-by: Dmitry Vyukov <dvyukov@...gle.com>
> >> Cc: Jakub Kicinski <jakub.kicinski@...ronome.com>
> >> Cc: Simon Horman <simon.horman@...ronome.com>
> >> Cc: Quentin Monnet <quentin.monnet@...ronome.com>
> >> Cc: Daniel Borkmann <daniel@...earbox.net>
> >> Signed-off-by: Hillf Danton <hdanton@...a.com>
> >> ---
> >>
> >> --- a/drivers/net/netdevsim/netdev.c
> >> +++ b/drivers/net/netdevsim/netdev.c
> >> @@ -296,6 +296,7 @@ nsim_create(struct nsim_dev *nsim_dev, s
> >>         dev_net_set(dev, nsim_dev_net(nsim_dev));
> >>         ns = netdev_priv(dev);
> >>         ns->netdev = dev;
> >> +       u64_stats_init(&ns->syncp);
> >>         ns->nsim_dev = nsim_dev;
> >>         ns->nsim_dev_port = nsim_dev_port;
> >>         ns->nsim_bus_dev = nsim_dev->nsim_bus_dev;

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