Date:	Mon, 21 Sep 2015 10:09:49 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Scott Feldman <sfeldma@...il.com>
Cc:	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Ido Schimmel <idosch@...lanox.com>, eladr@...lanox.com,
	Florian Fainelli <f.fainelli@...il.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
Subject: Re: [patch net-next RFC 0/6] switchdev: introduce tranction enfra
 and for pre-commit split

Mon, Sep 21, 2015 at 09:23:24AM CEST, sfeldma@...il.com wrote:
>On Sat, Sep 19, 2015 at 5:29 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>> Jiri Pirko (6):
>>   switchdev: rename "trans" to "trans_ph".
>>   switchdev: introduce transaction infrastructure for attr_set and
>>     obj_add
>>   rocker: switch to local transaction phase enum
>>   switchdev: move transaction phase enum under transaction structure
>>   rocker: use switchdev transaction queue for allocated memory
>>   switchdev: split commit and prepare phase into two callbacks
>
>Patches compile, but first test bombs.  Cut-and-paste of dump at end
>of this email.

Told you :)


>
>I'm not sure I'm liking this patchset because it looks like a way for
>switchdev drivers to easily opt-out of the prepare-commit transaction
>model by simply not implementing the *_pre op.  I would rather drivers
>explicitly handle the PREPARE phase in code, even if that means
>skipping it gracefully (in code) with a comment (in code) explaining
>why it does not matter for this device/operation.  That's what DSA had
>done, mostly because it was a retro-fit.

Each driver should handle this inside it. If it does not need prepare
state, it simply does not implement it. That is the same for all cb,
ndos, netdev notifiers, etc. It is much cleaner and nicer to have these as
separate callbacks. Implementing multiple callback in one is just ugly,
sorry.


>
>Also, the patchset removes the ABORT callback in case of a rollback
>due to a failed PREPARE.  We can't make the assumption that it's just
>a memory list to destroy on ABORT.  The driver, on PREPARE, may have
>reserved device space or staged an operation on the device which we'll
>need to undo on ABORT.

Yep, just register an item with custom destructor, there you can do
whatever. Also, I believe much nicer comparing to current code.


>
>So we need ABORT back, and we need PREPARE to not be optional, so
>what's left list enqueue/dequeue helpers, which I'm not seeing much
>value in up-leveling as the driver can do list_add/del itself.

Why would every driver do it itself, over and over when there can be a
clean infrastructure to do that. Including abort phase. Without the driver
needed to be involved.


>
>Am I missing something?  I didn't see a motivation statement for the
>RFC so I'm not sure where you wanted to take this.

I want to make current code much nicer, easier to read and implement in
other drivers. Look at rocker.c and how often there is == PREPARE there.
It's nearly impossible to followthe code, sorry.

My next patchset is to un-mess rocker.c (that freaking ofdpa stuff is everywhere)


>
>-scott
>
>
>
>[    1.998791] BUG: unable to handle kernel NULL pointer dereference
>at 0000000000000008
>[    2.000005] IP: [<ffffffffa005a2c5>]
>rocker_port_kzalloc.isra.50+0x5/0x10 [rocker]
>[    2.000005] PGD 0
>[    2.000005] Oops: 0000 [#1] SMP
>[    2.000005] Modules linked in: floppy(+) ata_piix(+) libata
>rocker(+) virtio_pci(+) virtio_ring virtio scsi_mod
>[    2.000005] CPU: 0 PID: 91 Comm: modprobe Not tainted 4.2.0+ #3
>[    2.000005] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
>BIOS rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
>[    2.000005] task: ffff88000f5e0800 ti: ffff88000f5f8000 task.ti:
>ffff88000f5f8000
>[    2.000005] RIP: 0010:[<ffffffffa005a2c5>]  [<ffffffffa005a2c5>]
>rocker_port_kzalloc.isra.50+0x5/0x10 [rocker]
>[    2.000005] RSP: 0018:ffff88000f5fba20  EFLAGS: 00010246
>[    2.000005] RAX: ffff88000f17c050 RBX: ffff88000b400000 RCX: 0000000000000020
>[    2.000005] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
>[    2.000005] RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffffa0058680
>[    2.000005] R10: 0000000000000001 R11: 0000000000009319 R12: 0000000000000000
>[    2.000005] R13: ffff88000f5b7000 R14: ffff88000f5b7840 R15: 0000000000000000
>[    2.000005] FS:  00007fd132237700(0000) GS:ffff88000fc00000(0000)
>knlGS:0000000000000000
>[    2.000005] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>[    2.000005] CR2: 0000000000000008 CR3: 000000000f5d5000 CR4: 00000000000006f0
>[    2.000005] Stack:
>[    2.000005]  ffffffffa005a32a 0000000000000001 00ff88000f5b7000
>ffffffff8175725a
>[    2.000005]  ffffffffa0057750 0000000000000000 ffffffffa0058680
>000000200000001a
>[    2.000005]  ffff88000b400000 0000000000000000 ffff88000ea06000
>ffff88000f5b7000
>[    2.000005] Call Trace:
>[    2.000005]  [<ffffffffa005a32a>] ? rocker_cmd_exec+0x5a/0x1f0 [rocker]
>[    2.000005]  [<ffffffffa0057750>] ?
>rocker_cmd_get_port_stats_prep+0x90/0x90 [rocker]
>[    2.000005]  [<ffffffffa0058680>] ?
>rocker_cmd_get_port_settings_phys_name_proc+0xb0/0xb0 [rocker]
>[    2.000005]  [<ffffffffa005e37a>] ? rocker_probe+0xb6a/0xe59 [rocker]
>[    2.000005]  [<ffffffff812b6608>] ? local_pci_probe+0x48/0xa0
>[    2.000005]  [<ffffffff812b7142>] ? pci_device_probe+0x112/0x130
>[    2.000005]  [<ffffffff81384b46>] ? driver_probe_device+0x196/0x2a0
>[    2.000005]  [<ffffffff81384c50>] ? driver_probe_device+0x2a0/0x2a0
>[    2.000005]  [<ffffffff81384cdd>] ? __driver_attach+0x8d/0x90
>[    2.000005]  [<ffffffff81384c50>] ? driver_probe_device+0x2a0/0x2a0
>[    2.000005]  [<ffffffff81382f3c>] ? bus_for_each_dev+0x4c/0x80
>[    2.000005]  [<ffffffff81384219>] ? bus_add_driver+0x119/0x220
>[    2.000005]  [<ffffffffa0065000>] ? 0xffffffffa0065000
>[    2.000005]  [<ffffffff813854ba>] ? driver_register+0x5a/0xe0
>[    2.000005]  [<ffffffffa0065000>] ? 0xffffffffa0065000
>[    2.000005]  [<ffffffffa0065033>] ? rocker_module_init+0x33/0x1000 [rocker]
>[    2.000005]  [<ffffffff81002110>] ? do_one_initcall+0x90/0x1e0
>[    2.000005]  [<ffffffff81110bd0>] ? do_init_module+0x50/0x1d8
>[    2.000005]  [<ffffffff810d632c>] ? load_module+0x1c1c/0x2240
>[    2.000005]  [<ffffffff810d33e0>] ? show_initstate+0x50/0x50
>[    2.000005]  [<ffffffff810d6a54>] ? SyS_init_module+0x104/0x130
>[    2.000005]  [<ffffffff81508ef6>] ? entry_SYSCALL_64_fastpath+0x16/0x75
>[    2.000005] Code: 48 89 c1 48 c7 c2 10 dc 15 81 48 89 c6 e8 e4 0d
>4a e1 48 8b 3b e8 1c 1b 4a e1 eb b6 66 2e 0f 1f 84 00 00 00 00 00 48
>89 d1 89 f2 <8b> 77 08 e9 73 ff ff ff 0f 1f 00 48 83 ec 68 4c 89 7c 24
>60 41
>[    2.000005] RIP  [<ffffffffa005a2c5>]
>rocker_port_kzalloc.isra.50+0x5/0x10 [rocker]
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