Messages in this thread | | | Date | Sat, 03 Oct 2020 18:54:02 +0200 | From | Michael Walle <> | Subject | Re: [PATCH] mtd: spi-nor: Prefer asynchronous probe |
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Hi Douglas,
Am 2020-10-03 18:27, schrieb Doug Anderson: > Hi, > > On Sat, Oct 3, 2020 at 8:22 AM Michael Walle <michael@walle.cc> wrote: >> >> Hi Douglas, >> >> > On my system the spi_nor_probe() took ~6 ms at bootup. That's not a >> > lot, but every little bit adds up to a slow bootup. While we can get >> > this out of the boot path by making it a module, there are times where >> > it is convenient (or even required) for this to be builtin the kernel. >> > Let's set that we prefer async probe so that we don't block other >> > drivers from probing while we are probing. >> > >> > This is a tiny little change that is almost guaranteed to be safe for >> > anything that is able to run as a module, which SPI_NOR is. >> > Specifically modules are already probed asynchronously. Also: since >> > other things in the system may have enabled asynchronous probe the >> > system may already be doing other things during our probe. >> > >> > There is a small possibility that some other driver that was a client >> > of SPI_NOR didn't handle -EPROBE_DEFER and was relying on probe >> > ordering and only worked when the SPI_NOR and the SPI bus were >> > builtin. In that case the other driver has a bug that's waiting to >> > hit and the other driver should be fixed. >> >> linux-next now triggers the following warning in kernel/kmod.c:136 on >> my >> board. I've bisected this to this patch. >> >> kmod.c: >> /* >> * We don't allow synchronous module loading from async. >> Module >> * init may invoke async_synchronize_full() which will end up >> * waiting for this task which already is waiting for the >> module >> * loading to complete, leading to a deadlock. >> */ >> WARN_ON_ONCE(wait && current_is_async()); >> >> [ 1.849801] ------------[ cut here ]------------ >> [ 1.854271] mscc_felix 0000:00:00.5: device is disabled, skipping >> [ 1.858753] WARNING: CPU: 1 PID: 7 at kernel/kmod.c:136 >> __request_module+0x3a4/0x568 >> [ 1.858755] Modules linked in: >> [ 1.865028] fsl_enetc 0000:00:00.0: Adding to iommu group 1 >> [ 1.872640] CPU: 1 PID: 7 Comm: kworker/u4:0 Not tainted >> 5.9.0-rc6-00001-g03edda0e1eda #113 >> [ 1.872642] Hardware name: Kontron SMARC-sAL28 (Single PHY) on >> SMARC Eval 2.0 carrier (DT) >> [ 1.872647] Workqueue: events_unbound async_run_entry_fn >> [ 1.876013] spi-nor spi0.0: w25q32dw (4096 Kbytes) >> [ 1.881294] pstate: 00000005 (nzcv daif -PAN -UAO BTYPE=--) >> [ 1.881297] pc : __request_module+0x3a4/0x568 >> [ 1.881299] lr : __request_module+0x39c/0x568 >> [ 1.881302] sp : ffff8000113a3920 >> [ 1.925739] x29: ffff8000113a3920 x28: ffff800010c7b000 >> [ 1.931068] x27: ffff00207ae05648 x26: ffff800010a41a88 >> [ 1.936397] x25: 0000000000000000 x24: 0000000000000000 >> [ 1.941727] x23: ffff800010c35140 x22: 0000000000000001 >> [ 1.947055] x21: ffff800011149948 x20: ffff800010615bdc >> [ 1.952383] x19: 00000000ffffffff x18: 0000000000000000 >> [ 1.957447] fsl_enetc 0000:00:00.0: enabling device (0400 -> 0402) >> [ 1.957711] x17: ffff800010a3e618 x16: ffff800010a3e5f8 >> [ 1.964175] libphy: Freescale ENETC MDIO Bus: probed >> [ 1.969238] x15: ffffffffffffffff x14: ffff800011149948 >> [ 1.969241] x13: ffff8000113a3918 x12: 0000000000000018 >> [ 1.969245] x11: 0000000000000005 x10: 0101010101010101 >> [ 1.975241] 10 fixed-partitions partitions found on MTD device >> 20c0000.spi >> [ 1.979550] x9 : ffff80001005f6a4 x8 : 0000000000000000 >> [ 1.979553] x7 : 606f2c6364776865 x6 : 05041c090d431511 >> [ 1.979556] x5 : 1115430d091c0405 x4 : 0000000000000000 >> [ 1.979558] x3 : 6dac8d8d2dccae00 x2 : ffff800010c956e8 >> [ 1.979561] x1 : ffff80001005fa58 x0 : 0000000000000001 >> [ 1.979564] Call trace: >> [ 1.979571] __request_module+0x3a4/0x568 >> [ 1.984914] Creating 10 MTD partitions on "20c0000.spi": >> [ 1.990227] parse_mtd_partitions+0x2ec/0x3c0 >> [ 1.990232] mtd_device_parse_register+0xdc/0x1c8 >> [ 1.997133] 0x000000000000-0x000000010000 : "rcw" >> [ 2.002454] spi_nor_probe+0x29c/0x2f0 >> [ 2.002458] spi_mem_probe+0x74/0xb0 >> [ 2.017759] 0x000000010000-0x000000100000 : "failsafe bootloader" >> [ 2.018433] spi_drv_probe+0x88/0xe8 >> [ 2.018439] really_probe+0xec/0x3c0 >> [ 2.033744] 0x000000100000-0x000000140000 : "failsafe DP firmware" >> [ 2.035555] driver_probe_device+0x60/0xc0 >> [ 2.035559] __device_attach_driver+0x8c/0xd0 >> [ 2.040455] 0x000000140000-0x0000001e0000 : "failsafe trusted >> firmware" >> [ 2.044642] bus_for_each_drv+0x84/0xd8 >> [ 2.044645] __device_attach_async_helper+0xc4/0xe8 >> [ 2.044648] async_run_entry_fn+0x4c/0x150 >> [ 2.044653] process_one_work+0x1f4/0x4b8 >> [ 2.057751] 0x0000001e0000-0x000000200000 : "reserved" >> [ 2.062814] worker_thread+0x50/0x480 >> [ 2.062817] kthread+0x160/0x168 >> [ 2.062821] ret_from_fork+0x10/0x34 >> [ 2.073748] 0x000000200000-0x000000210000 : "configuration store" >> [ 2.076185] ---[ end trace 44224cc02e4e53d2 ]--- >> >> -michael > > Thanks for your report! My vote would be to revert my patch and then > this would need to be resolved before it could be added back in. > Without doing tons of research, maybe the right answer here is that > mtd_device_parse_register() should be moved into a separate task so > it's not blocking probe? I probably won't try to tackle this > immediately, but the eventual goal is that async is default, so I > think this would need to be resolved before then.
Ok. Vignesh, will you take care of that?
While debugging another issue I also noticed that sometimes my /dev/mtdN devices were reordered. Note that I have two SPI flashes. Might this also be connected to the async probe?
-michael
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