Re: [patch 03/10] genirq/msi: Make MSI descriptor alloc/free ready for range allocations

[Marc Zyngier <maz@kernel.org>]

On Sat, 27 Nov 2021 01:24:34 +0000,
Thomas Gleixner <tglx@linutronix.de> wrote:
> 
> Convert the MSI descriptor related functions to ranges and fixup the call
> sites.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  drivers/base/platform-msi.c |    3 ++-
>  include/linux/msi.h         |    7 ++++---
>  kernel/irq/msi.c            |   38 +++++++++++++++++++-------------------
>  3 files changed, 25 insertions(+), 23 deletions(-)

This particular patch breaks one of my test boxes when allocating the
MSIs for the first SMMUv3 it encounters:

[   14.700206] arm-smmu-v3 arm-smmu-v3.0.auto: option mask 0x0
[   14.705848] arm-smmu-v3 arm-smmu-v3.0.auto: ias 48-bit, oas 48-bit (features 0x00041fff)
[   14.716184] arm-smmu-v3 arm-smmu-v3.0.auto: allocated 65536 entries for cmdq
[   14.723285] arm-smmu-v3 arm-smmu-v3.0.auto: allocated 128 entries for evtq
[   14.730170] arm-smmu-v3 arm-smmu-v3.0.auto: allocated 256 entries for priq
[   41.282305] watchdog: BUG: soft lockup - CPU#43 stuck for 26s! [swapper/0:1]
[   41.289383] Modules linked in:
[   41.292430] irq event stamp: 3906684
[   41.295994] hardirqs last  enabled at (3906683): [<ffffb73f677c54d8>] ___slab_alloc+0x7c8/0x8c0
[   41.304698] hardirqs last disabled at (3906684): [<ffffb73f6806d478>] el1_interrupt+0x38/0xb0
[   41.313220] softirqs last  enabled at (3798058): [<ffffb73f6746099c>] __do_softirq+0x40c/0x58c
[   41.321825] softirqs last disabled at (3798053): [<ffffb73f674ee610>] __irq_exit_rcu+0x120/0x160
[   41.330607] CPU: 43 PID: 1 Comm: swapper/0 Not tainted 5.16.0-rc2-00078-g76af42494903 #41
[   41.338775] Hardware name: WIWYNN Mt.Jade Server System B81.030Z1.0007/Mt.Jade Motherboard, BIOS 1.3.20210110 2021/01/10
[   41.349634] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   41.356585] pc : lock_is_held_type+0x124/0x20c
[   41.361019] lr : lock_is_held_type+0xe8/0x20c
[   41.365365] sp : ffff80001051b840
[   41.368669] pmr_save: 000000e0
[   41.371712] x29: ffff80001051b840 x28: ffff000034d80000 x27: ffff07ff87606600
[   41.378838] x26: 00000000000000e0 x25: 00000000ffffffff x24: ffffb73f68733d00
[   41.385964] x23: 0000000000000028 x22: ffff07ff87606fb8 x21: ffffb73f68bffc38
[   41.393090] x20: ffff07ff87606fe0 x19: 0000000000000002 x18: 0000000000000014
[   41.400217] x17: 0000000076a13aac x16: 00000000486de301 x15: 00000000ed5ff5e1
[   41.407342] x14: 00000000fda7b077 x13: 0000000000000006 x12: 00000000b82b73dd
[   41.414468] x11: ffff07ff87606fb8 x10: ffffb73f6952d000 x9 : ffffb73f675a3750
[   41.421594] x8 : 0000000000000000 x7 : ffffb73f68e16000 x6 : ffffb73f677c6d64
[   41.428720] x5 : 0000000000000000 x4 : 0000000000000001 x3 : 000000000000ffff
[   41.435846] x2 : ffff50ff17454000 x1 : 0000000000000000 x0 : 0000000000000000
[   41.442972] Call trace:
[   41.445407]  lock_is_held_type+0x124/0x20c
[   41.449494]  rcu_read_lock_sched_held+0x68/0xac
[   41.454018]  trace_lock_acquire+0x78/0x1c0
[   41.458107]  lock_acquire+0x40/0x90
[   41.461585]  fs_reclaim_acquire+0x90/0x114
[   41.465676]  kmem_cache_alloc_trace+0x80/0x300
[   41.470110]  msi_add_simple_msi_descs+0x70/0x150
[   41.474718]  msi_domain_alloc_irqs_descs_locked+0x90/0xfc
[   41.480106]  msi_domain_alloc_irqs+0x58/0xa0
[   41.484364]  platform_msi_domain_alloc_irqs+0x5c/0xa0
[   41.489410]  arm_smmu_device_probe+0xfc0/0x1230
[   41.493936]  platform_probe+0x74/0xe4
[   41.497590]  really_probe+0xc4/0x470
[   41.501156]  __driver_probe_device+0x11c/0x190
[   41.505589]  driver_probe_device+0x48/0x110
[   41.509761]  __driver_attach+0xe0/0x200
[   41.513585]  bus_for_each_dev+0x7c/0xe0
[   41.517412]  driver_attach+0x30/0x3c
[   41.520976]  bus_add_driver+0x150/0x230
[   41.524801]  driver_register+0x84/0x140
[   41.528626]  __platform_driver_register+0x34/0x40
[   41.533319]  arm_smmu_driver_init+0x2c/0x38
[   41.537496]  do_one_initcall+0x80/0x3d0
[   41.541321]  kernel_init_freeable+0x318/0x3a0
[   41.545672]  kernel_init+0x30/0x14c
[   41.549151]  ret_from_fork+0x10/0x20

The issue seems to be originating in the previous patch, where the
following line was added:

+	struct msi_range range = { .first = 0, .last = UINT_MAX, .ndesc = nvec, };

In that context, only 'ndesc' was used, and that was fine.

However, in the current patch, ndesc use is removed, only first/last
are considered, and UINT_MAX is... a lot of MSIs.

This fixes it:

diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
index bef5b74a7268..a520bfd94a56 100644
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -975,7 +975,7 @@ int msi_domain_alloc_irqs_descs_locked(struct irq_domain *domain, struct device
  */
 int msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev, int nvec)
 {
-	struct msi_range range = { .first = 0, .last = UINT_MAX, .ndesc = nvec, };
+	struct msi_range range = { .first = 0, .last = nvec - 1, .ndesc = nvec, };
 	int ret;
 
 	msi_lock_descs(dev);

However, it'd be good to clarify the use of range->ndesc.

[...]

> --- a/kernel/irq/msi.c
> +++ b/kernel/irq/msi.c
> @@ -101,19 +101,19 @@ int msi_add_msi_desc(struct device *dev,
>   *
>   * Return: 0 on success or an appropriate failure code.
>   */
> -static int msi_add_simple_msi_descs(struct device *dev, unsigned int index, unsigned int ndesc)
> +static int msi_add_simple_msi_descs(struct device *dev, struct msi_range *range)

nit: most of the functions changed in this patch need to have their
documentation tidied up.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.