7095c97345
We can enter a deadlock situation because there is no sufficient protection
when ndo_get_stats64() runs in process context to guard against RX or TX NAPI
contexts running in softirq, this can lead to the following lockdep splat and
actual deadlock was experienced as well with an iperf session in the background
and a while loop doing ifconfig + ethtool.
[ 5.780350] ================================
[ 5.784679] WARNING: inconsistent lock state
[ 5.789011] 4.13.0-rc7-02179-g32fae27c725d #70 Not tainted
[ 5.794561] --------------------------------
[ 5.798890] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
[ 5.804971] swapper/0/0 [HC0[0]:SC1[1]:HE0:SE0] takes:
[ 5.810175] (&syncp->seq#2){+.?...}, at: [<c0768a28>] bcm_sysport_tx_reclaim+0x30/0x54
[ 5.818327] {SOFTIRQ-ON-W} state was registered at:
[ 5.823278] bcm_sysport_get_stats64+0x17c/0x258
[ 5.828053] dev_get_stats+0x38/0xac
[ 5.831776] rtnl_fill_stats+0x30/0x118
[ 5.835761] rtnl_fill_ifinfo+0x538/0xe24
[ 5.839921] rtmsg_ifinfo_build_skb+0x6c/0xd8
[ 5.844430] rtmsg_ifinfo_event.part.5+0x14/0x44
[ 5.849201] rtmsg_ifinfo+0x20/0x28
[ 5.852837] register_netdevice+0x628/0x6b8
[ 5.857171] register_netdev+0x14/0x24
[ 5.861051] bcm_sysport_probe+0x30c/0x438
[ 5.865280] platform_drv_probe+0x50/0xb0
[ 5.869418] driver_probe_device+0x2e8/0x450
[ 5.873817] __driver_attach+0x104/0x120
[ 5.877871] bus_for_each_dev+0x7c/0xc0
[ 5.881834] bus_add_driver+0x1b0/0x270
[ 5.885797] driver_register+0x78/0xf4
[ 5.889675] do_one_initcall+0x54/0x190
[ 5.893646] kernel_init_freeable+0x144/0x1d0
[ 5.898135] kernel_init+0x8/0x110
[ 5.901665] ret_from_fork+0x14/0x2c
[ 5.905363] irq event stamp: 24263
[ 5.908804] hardirqs last enabled at (24262): [<c08eecf0>] net_rx_action+0xc4/0x4e4
[ 5.916624] hardirqs last disabled at (24263): [<c0a7da00>] _raw_spin_lock_irqsave+0x1c/0x98
[ 5.925143] softirqs last enabled at (24258): [<c022a7fc>] irq_enter+0x84/0x98
[ 5.932524] softirqs last disabled at (24259): [<c022a918>] irq_exit+0x108/0x16c
[ 5.939985]
[ 5.939985] other info that might help us debug this:
[ 5.946576] Possible unsafe locking scenario:
[ 5.946576]
[ 5.952556] CPU0
[ 5.955031] ----
[ 5.957506] lock(&syncp->seq#2);
[ 5.960955] <Interrupt>
[ 5.963604] lock(&syncp->seq#2);
[ 5.967227]
[ 5.967227] *** DEADLOCK ***
[ 5.967227]
[ 5.973222] 1 lock held by swapper/0/0:
[ 5.977092] #0: (&(&ring->lock)->rlock){..-...}, at: [<c0768a18>] bcm_sysport_tx_reclaim+0x20/0x54
So just remove the u64_stats_update_begin()/end() pair in ndo_get_stats64()
since it does not appear to be useful for anything. No inconsistency was
observed with either ifconfig or ethtool, global TX counts equal the sum of
per-queue TX counts on a 32-bit architecture.
Fixes:
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.