Re: [PATCH v8] mm: cma: support sysfs

[Minchan Kim]

On Fri, Mar 26, 2021 at 02:59:30PM +0100, Anders Roxell wrote:
> On Thu, 25 Mar 2021 at 00:09, Minchan Kim <minchan@xxxxxxxxxx> wrote:
> >
> > Since CMA is getting used more widely, it's more important to
> > keep monitoring CMA statistics for system health since it's
> > directly related to user experience.
> >
> > This patch introduces sysfs statistics for CMA, in order to provide
> > some basic monitoring of the CMA allocator.
> >
> >  * the number of CMA page successful allocations
> >  * the number of CMA page allocation failures
> >
> > These two values allow the user to calcuate the allocation
> > failure rate for each CMA area.
> >
> > e.g.)
> >   /sys/kernel/mm/cma/WIFI/alloc_pages_[success|fail]
> >   /sys/kernel/mm/cma/SENSOR/alloc_pages_[success|fail]
> >   /sys/kernel/mm/cma/BLUETOOTH/alloc_pages_[success|fail]
> >
> > The cma_stat was intentionally allocated by dynamic allocation
> > to harmonize with kobject lifetime management.
> > https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@xxxxxxxxx/
> >
> > Tested-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > Reviewed-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
> > Link: https://lore.kernel.org/linux-mm/20210316100433.17665-1-colin.king@xxxxxxxxxxxxx/
> > Addresses-Coverity: ("Dereference after null check")
> > Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> 
> When I build an arm64 kernel (allmodconfig - boot selftest) on today's
> next tag: next-20210326, I see this issue when I'm booting in qemu.
> 
> [    0.985891][    T9] Callback from call_rcu_tasks() invoked.
> [    1.008860][    T1] smp: Bringing up secondary CPUs ...
> [    1.012655][    T1] smp: Brought up 1 node, 1 CPU
> [    1.015194][    T1] SMP: Total of 1 processors activated.
> [    1.018987][    T1] CPU features: detected: 32-bit EL0 Support
> [    1.021995][    T1] CPU features: detected: CRC32 instructions
> [    1.026047][    T1] CPU features: detected: 32-bit EL1 Support
> [    1.033728][    T1] CPU features: emulated: Privileged Access Never
> (PAN) using TTBR0_EL1 switching
> [    2.140828][    T1] CPU: All CPU(s) started at EL1
> [    2.144773][   T17] alternatives: patching kernel code
> [  132.866390][    C0] watchdog: BUG: soft lockup - CPU#0 stuck for
> 25s! [pgdatinit0:20]
> [  132.870865][    C0] Modules linked in:
> [  132.873037][    C0] irq event stamp: 739758
> [  132.875308][    C0] hardirqs last  enabled at (739757):
> [<ffff8000126fb3d0>] _raw_spin_unlock_irqrestore+0x90/0x100
> [  132.880740][    C0] hardirqs last disabled at (739758):
> [<ffff8000126e30a4>] enter_el1_irq_or_nmi+0xa4/0xc0
> [  132.885801][    C0] softirqs last  enabled at (739056):
> [<ffff800010010f98>] __do_softirq+0x8b8/0x9ac
> [  132.890571][    C0] softirqs last disabled at (739051):
> [<ffff80001013742c>] __irq_exit_rcu+0x1ac/0x240
> [  132.895560][    C0] CPU: 0 PID: 20 Comm: pgdatinit0 Not tainted
> 5.12.0-rc4-next-20210326-00008-g23921ff47279 #1
> [  132.900759][    C0] Hardware name: linux,dummy-virt (DT)
> [  132.903637][    C0] pstate: 40400005 (nZcv daif +PAN -UAO -TCO BTYPE=--)
> [  132.907212][    C0] pc : _raw_spin_unlock_irqrestore+0xa4/0x100
> [  132.910432][    C0] lr : _raw_spin_unlock_irqrestore+0x90/0x100
> [  132.913647][    C0] sp : ffff000007b9f640
> [  132.915832][    C0] x29: ffff000007b9f640 x28: ffff800016954518
> [  132.919237][    C0] x27: 000000000000000e x26: dead000000000100
> [  132.922689][    C0] x25: dead000000000122 x24: 00000000000559b0
> [  132.926098][    C0] x23: ffff80001550e000 x22: ffff800016954530
> [  132.929479][    C0] x21: ffff800016954518 x20: 0000000000000000
> [  132.932901][    C0] x19: ffff800010f662f4 x18: 0000000000001530
> [  132.936312][    C0] x17: 0000000000001470 x16: 0000000000005518
> [  132.939723][    C0] x15: 0000000000001578 x14: ffff800010189520
> [  132.943107][    C0] x13: ffff8000107592e0 x12: ffff600000f73eb1
> [  132.946520][    C0] x11: 1fffe00000f73eb0 x10: ffff600000f73eb0
> [  132.949914][    C0] x9 : dfff800000000000 x8 : ffff000007b9f587
> [  132.953312][    C0] x7 : 0000000000000001 x6 : 00009fffff08c150
> [  132.956713][    C0] x5 : 0000000000000000 x4 : 0000000000000000
> [  132.960117][    C0] x3 : ffff000007b90040 x2 : 000000000005e6fd
> [  132.963521][    C0] x1 : 00000000000000c0 x0 : 0000000000000080
> [  132.966889][    C0] Call trace:
> [  132.968667][    C0]  _raw_spin_unlock_irqrestore+0xa4/0x100
> [  132.971754][    C0]  __debug_check_no_obj_freed+0x1d4/0x2a0
> [  132.974890][    C0]  debug_check_no_obj_freed+0x20/0x80
> [  132.977813][    C0]  __free_pages_ok+0x5a0/0x740
> [  132.980384][    C0]  __free_pages_core+0x24c/0x280
> [  132.983091][    C0]  deferred_free_range+0x6c/0xbc
> [  132.985826][    C0]  deferred_init_maxorder+0x2d0/0x350
> [  132.988735][    C0]  deferred_init_memmap_chunk+0xc8/0x124
> [  132.991784][    C0]  padata_do_multithreaded+0x15c/0x578
> [  132.994723][    C0]  deferred_init_memmap+0x26c/0x364
> [  132.997560][    C0]  kthread+0x23c/0x260
> [  132.999851][    C0]  ret_from_fork+0x10/0x18
> [  133.002324][    C0] Kernel panic - not syncing: softlockup: hung tasks
> [  133.005767][    C0] CPU: 0 PID: 20 Comm: pgdatinit0 Tainted: G
>        L    5.12.0-rc4-next-20210326-00008-g23921ff47279 #1
> [  133.011613][    C0] Hardware name: linux,dummy-virt (DT)
> [  133.014435][    C0] Call trace:
> [  133.016143][    C0]  dump_backtrace+0x0/0x420
> [  133.018617][    C0]  show_stack+0x38/0x60
> [  133.020882][    C0]  dump_stack+0x1fc/0x2c8
> [  133.023343][    C0]  panic+0x304/0x5d8
> [  133.025567][    C0]  watchdog_timer_fn+0x4ac/0x500
> [  133.028209][    C0]  __run_hrtimer+0x770/0xba0
> [  133.030734][    C0]  __hrtimer_run_queues+0x1a0/0x220
> [  133.033537][    C0]  hrtimer_run_queues+0x20c/0x240
> [  133.036202][    C0]  update_process_times+0xbc/0x1a0
> [  133.038997][    C0]  tick_periodic+0x27c/0x2c0
> [  133.041510][    C0]  tick_handle_periodic+0x44/0x120
> [  133.044267][    C0]  arch_timer_handler_virt+0x68/0xa0
> [  133.047226][    C0]  handle_percpu_devid_irq+0x118/0x2a0
> [  133.050229][    C0]  __handle_domain_irq+0x150/0x1c0
> [  133.052959][    C0]  gic_handle_irq+0x130/0x180
> [  133.055505][    C0]  el1_irq+0xc0/0x15c
> [  133.057723][    C0]  _raw_spin_unlock_irqrestore+0xa4/0x100
> [  133.060792][    C0]  __debug_check_no_obj_freed+0x1d4/0x2a0
> [  133.063869][    C0]  debug_check_no_obj_freed+0x20/0x80
> [  133.066813][    C0]  __free_pages_ok+0x5a0/0x740
> [  133.069409][    C0]  __free_pages_core+0x24c/0x280
> [  133.072127][    C0]  deferred_free_range+0x6c/0xbc
> [  133.074847][    C0]  deferred_init_maxorder+0x2d0/0x350
> [  133.077803][    C0]  deferred_init_memmap_chunk+0xc8/0x124
> [  133.080834][    C0]  padata_do_multithreaded+0x15c/0x578
> [  133.083791][    C0]  deferred_init_memmap+0x26c/0x364
> [  133.086614][    C0]  kthread+0x23c/0x260
> [  133.088879][    C0]  ret_from_fork+0x10/0x18
> [  133.092092][    C0] ---[ end Kernel panic - not syncing:
> softlockup: hung tasks ]---
> 
> Full log [1], and my .config [2].
> 
> I bisected down to patch 799815f497e2 ("mm: cma: support sysfs").
> 
> When I revert
> 799815f497e2 ("mm: cma: support sysfs")
> 7af97692f30d ("mm: cma: fix potential null dereference on pointer cma")
> 
> The kernel boots fine.
> 
> Any idea whats happening?

Hi Anders,

Dmitry reported the crash(However, your callstack is not the same
and didn't show any CMA stuffs so I am not sure it's same crash)
and posted the fix.

https://lore.kernel.org/linux-mm/20210324192044.1505747-1-minchan@xxxxxxxxxx/

However, in the end, it was folded into original patchset to replace it.
That is an this v8 patch. So, could you try it?

1. revert 7af97692f30d ("mm: cma: fix potential null dereference on pointer cma")
2. revert 799815f497e2 ("mm: cma: support sysfs")
3. apply this v8 patch.

Thank you.




> 
> Cheers,
> Anders
> [1] http://ix.io/2U9S
> [2] http://ix.io/2Ua3