Messages in this thread | | | Date | Tue, 19 Feb 2019 08:26:43 -0800 | From | Guenter Roeck <> | Subject | Re: [PATCH 2/2] exec: increase BINPRM_BUF_SIZE to 256 |
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On Tue, Feb 19, 2019 at 01:37:57PM +0100, Oleg Nesterov wrote: > On 02/18, Guenter Roeck wrote: > > > > Unfortunately, this patch causes one of my qemu emulations to crash. > > The crash is not always seen, but at least with every other boot attempt. > > Hmm. I can't imagine how this change can cause the null-ptr-deref in > blk_mq_run_hw_queue(). > Me not either.
> > Reverting the patch fixes the problem. Crash log and bisect results > > are attached below. > > Do you mean that you applied the "revert" patch on top of linux-next ? > I reverted to patch on top of linux-next (next-20190218, more specifically). The problem was gone. I then reverted the revert and the probllem was back.
> Or did you rely on git-bisect ? > Sorry, I don't understand the question. git bisect, unless I am missing something, doesn't revert any patches.
> > [ 10.681671] BUG: Kernel NULL pointer dereference at 0x00000040 > > [ 10.681826] Faulting instruction address: 0xc0431480 > > [ 10.682072] Oops: Kernel access of bad area, sig: 11 [#1] > > [ 10.682251] BE PAGE_SIZE=4K PREEMPT Xilinx Virtex440 > > [ 10.682387] Modules linked in: > > [ 10.682528] CPU: 0 PID: 1 Comm: swapper Tainted: G W 5.0.0-rc6-next-20190218+ #2 > > [ 10.682733] NIP: c0431480 LR: c043147c CTR: c0422ad8 > > [ 10.682863] REGS: cf82fbe0 TRAP: 0300 Tainted: G W (5.0.0-rc6-next-20190218+) > > [ 10.683065] MSR: 00029000 <CE,EE,ME> CR: 22000222 XER: 00000000 > > [ 10.683236] DEAR: 00000040 ESR: 00000000 > > [ 10.683236] GPR00: c043147c cf82fc90 cf82ccc0 00000000 00000000 00000000 00000002 00000000 > > [ 10.683236] GPR08: 00000000 00000000 c04310bc 00000000 22000222 00000000 c0002c54 00000000 > > [ 10.683236] GPR16: 00000000 00000001 c09aa39c c09021b0 c09021dc 00000007 c0a68c08 00000000 > > [ 10.683236] GPR24: 00000001 ced6d400 ced6dcf0 c0815d9c 00000000 00000000 00000000 cedf0800 > > [ 10.684331] NIP [c0431480] blk_mq_run_hw_queue+0x28/0x114 > > [ 10.684473] LR [c043147c] blk_mq_run_hw_queue+0x24/0x114 > > [ 10.684602] Call Trace: > > [ 10.684671] [cf82fc90] [c043147c] blk_mq_run_hw_queue+0x24/0x114 (unreliable) > > [ 10.684854] [cf82fcc0] [c04315bc] blk_mq_run_hw_queues+0x50/0x7c > > [ 10.685002] [cf82fce0] [c0422b24] blk_set_queue_dying+0x30/0x68 > > [ 10.685154] [cf82fcf0] [c0423ec0] blk_cleanup_queue+0x34/0x14c > > [ 10.685306] [cf82fd10] [c054d73c] ace_probe+0x3dc/0x508 > > [ 10.685445] [cf82fd50] [c052d740] platform_drv_probe+0x4c/0xb8 > > [ 10.685592] [cf82fd70] [c052abb0] really_probe+0x20c/0x32c > > [ 10.685728] [cf82fda0] [c052ae58] driver_probe_device+0x68/0x464 > > [ 10.685877] [cf82fdc0] [c052b500] device_driver_attach+0xb4/0xe4 > > [ 10.686024] [cf82fde0] [c052b5dc] __driver_attach+0xac/0xfc > > [ 10.686161] [cf82fe00] [c0528428] bus_for_each_dev+0x80/0xc0 > > [ 10.686314] [cf82fe30] [c0529b3c] bus_add_driver+0x144/0x234 > > [ 10.686457] [cf82fe50] [c052c46c] driver_register+0x88/0x15c > > [ 10.686610] [cf82fe60] [c09de288] ace_init+0x4c/0xac > > [ 10.686742] [cf82fe80] [c0002730] do_one_initcall+0xac/0x330 > > [ 10.686888] [cf82fee0] [c09aafd0] kernel_init_freeable+0x34c/0x478 > > [ 10.687043] [cf82ff30] [c0002c6c] kernel_init+0x18/0x114 > > looks unrelated... >
Indeed...
The underlying problem is in the error handling code of ace_setup(), which calls put_disk() followed by blk_cleanup_queue(). put_disk() calls disk_release(), which calls blk_put_queue(), which in turn results in a call to blk_mq_hw_sysfs_release().
Added debug code, with your patch reverted, shows:
######### blk_mq_hw_sysfs_release hctx=cee4a800 ... ######### blk_mq_run_hw_queue hctx=cee4a800
blk_mq_hw_sysfs_release() calls kfree(htcx), so accessing it later is most definitely not a good idea.
No idea why this only causes problems with your patch applied.
I'll send a patch to fix the underlying problem.
Thanks, Guenter
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