On Thu, Oct 22, 2020 at 11:37:53AM +0530, Aneesh Kumar K.V wrote:
> commit 6f42193fd86e ("memremap: don't use a separate devm action for
> devmap_managed_enable_get") changed the static key updates such that we
> now call devmap_managed_enable_put() without doing the equivalent
> devmap_managed_enable_get().
>
> devmap_managed_enable_get() is only called for MEMORY_DEVICE_PRIVATE and
> MEMORY_DEVICE_FS_DAX, But memunmap_pages() get called for other pgmap
> types too. This results in the below warning when switching between
> system-ram and devdax mode for devdax namespace.
>
> jump label: negative count!
> WARNING: CPU: 52 PID: 1335 at kernel/jump_label.c:235
> static_key_slow_try_dec+0x88/0xa0
> Modules linked in:
> ....
>
> NIP [c000000000433318] static_key_slow_try_dec+0x88/0xa0
> LR [c000000000433314] static_key_slow_try_dec+0x84/0xa0
> Call Trace:
> [c000000025c1f660] [c000000000433314] static_key_slow_try_dec+0x84/0xa0
> (unreliable)
> [c000000025c1f6d0] [c000000000433664]
> __static_key_slow_dec_cpuslocked+0x34/0xd0
> [c000000025c1f700] [c0000000004337a4] static_key_slow_dec+0x54/0xf0
> [c000000025c1f770] [c00000000059c49c] memunmap_pages+0x36c/0x500
> [c000000025c1f820] [c000000000d91d10] devm_action_release+0x30/0x50
> [c000000025c1f840] [c000000000d92e34] release_nodes+0x2f4/0x3e0
> [c000000025c1f8f0] [c000000000d8b15c]
> device_release_driver_internal+0x17c/0x280
> [c000000025c1f930] [c000000000d883a4] bus_remove_device+0x124/0x210
> [c000000025c1f9b0] [c000000000d80ef4] device_del+0x1d4/0x530
> [c000000025c1fa70] [c000000000e341e8] unregister_dev_dax+0x48/0xe0
> [c000000025c1fae0] [c000000000d91d10] devm_action_release+0x30/0x50
> [c000000025c1fb00] [c000000000d92e34] release_nodes+0x2f4/0x3e0
> [c000000025c1fbb0] [c000000000d8b15c]
> device_release_driver_internal+0x17c/0x280
> [c000000025c1fbf0] [c000000000d87000] unbind_store+0x130/0x170
> [c000000025c1fc30] [c000000000d862a0] drv_attr_store+0x40/0x60
> [c000000025c1fc50] [c0000000006d316c] sysfs_kf_write+0x6c/0xb0
> [c000000025c1fc90] [c0000000006d2328] kernfs_fop_write+0x118/0x280
> [c000000025c1fce0] [c0000000005a79f8] vfs_write+0xe8/0x2a0
> [c000000025c1fd30] [c0000000005a7d94] ksys_write+0x84/0x140
> [c000000025c1fd80] [c00000000003a430] system_call_exception+0x120/0x270
> [c000000025c1fe20] [c00000000000c540] system_call_common+0xf0/0x27c
>
> Cc: Christoph Hellwig <[email protected]>
> Cc: Dan Williams <[email protected]>
> Cc: Sachin Sant <[email protected]>
> Cc: [email protected]
> Cc: Ira Weiny <[email protected]>
> Cc: Jason Gunthorpe <[email protected]>
> Signed-off-by: Aneesh Kumar K.V <[email protected]>
> ---
> mm/memremap.c | 19 +++++++++++++++----
> 1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 73a206d0f645..d4402ff3e467 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -158,6 +158,16 @@ void memunmap_pages(struct dev_pagemap *pgmap)
> {
> unsigned long pfn;
> int i;
> + bool need_devmap_managed = false;
> +
> + switch (pgmap->type) {
> + case MEMORY_DEVICE_PRIVATE:
> + case MEMORY_DEVICE_FS_DAX:
> + need_devmap_managed = true;
> + break;
> + default:
> + break;
> + }
Is it overkill to avoid duplicating this switch logic in
page_is_devmap_managed() by creating another call which can be used here?
>
> dev_pagemap_kill(pgmap);
> for (i = 0; i < pgmap->nr_range; i++)
> @@ -169,7 +179,8 @@ void memunmap_pages(struct dev_pagemap *pgmap)
> pageunmap_range(pgmap, i);
>
> WARN_ONCE(pgmap->altmap.alloc, "failed to free all reserved pages\n");
> - devmap_managed_enable_put();
> + if (need_devmap_managed)
> + devmap_managed_enable_put();
> }
> EXPORT_SYMBOL_GPL(memunmap_pages);
>
> @@ -307,7 +318,7 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
> .pgprot = PAGE_KERNEL,
> };
> const int nr_range = pgmap->nr_range;
> - bool need_devmap_managed = true;
> + bool need_devmap_managed = false;
I'm CC'ing Ralph Campbell because I think some of his work has proposed this
same change.
Ira
> int error, i;
>
> if (WARN_ONCE(!nr_range, "nr_range must be specified\n"))
> @@ -327,6 +338,7 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
> WARN(1, "Missing owner\n");
> return ERR_PTR(-EINVAL);
> }
> + need_devmap_managed = true;
> break;
> case MEMORY_DEVICE_FS_DAX:
> if (!IS_ENABLED(CONFIG_ZONE_DEVICE) ||
> @@ -334,13 +346,12 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
> WARN(1, "File system DAX not supported\n");
> return ERR_PTR(-EINVAL);
> }
> + need_devmap_managed = true;
> break;
> case MEMORY_DEVICE_GENERIC:
> - need_devmap_managed = false;
> break;
> case MEMORY_DEVICE_PCI_P2PDMA:
> params.pgprot = pgprot_noncached(params.pgprot);
> - need_devmap_managed = false;
> break;
> default:
> WARN(1, "Invalid pgmap type %d\n", pgmap->type);
> --
> 2.26.2
>
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