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SubjectRe: [PATCH v1] Revert "software node: Simplify software_node_release() function"
On Thu 2020-02-27 16:00:01, Brendan Higgins wrote:
> This reverts commit 3df85a1ae51f6b256982fe9d17c2dc5bfb4cc402.
>
> The reverted commit says "It's possible to release the node ID
> immediately when fwnode_remove_software_node() is called, no need to
> wait for software_node_release() with that." However, releasing the node
> ID before waiting for software_node_release() to be called causes the
> node ID to be released before the kobject and the underlying sysfs
> entry; this means there is a period of time where a sysfs entry exists
> that is associated with an unallocated node ID.
>
> Once consequence of this is that there is a race condition where it is
> possible to call fwnode_create_software_node() with no parent node
> specified (NULL) and have it fail with -EEXIST because the node ID that
> was assigned is still associated with a stale sysfs entry that hasn't
> been cleaned up yet.
>
> Although it is difficult to reproduce this race condition under normal
> conditions, it can be deterministically reproduced with the following
> minconfig on UML:
>
> CONFIG_KUNIT_DRIVER_PE_TEST=y
> CONFIG_DEBUG_KERNEL=y
> CONFIG_DEBUG_OBJECTS=y
> CONFIG_DEBUG_OBJECTS_TIMERS=y
> CONFIG_DEBUG_KOBJECT_RELEASE=y
> CONFIG_KUNIT=y
>
> Running the tests with this configuration causes the following failure:
>
> <snip>
> kobject: 'node0' ((____ptrval____)): kobject_release, parent (____ptrval____) (delayed 400)
> ok 1 - pe_test_uints
> sysfs: cannot create duplicate filename '/kernel/software_nodes/node0'
> CPU: 0 PID: 28 Comm: kunit_try_catch Not tainted 5.6.0-rc3-next-20200227 #14
> <snip>
> kobject_add_internal failed for node0 with -EEXIST, don't try to register things with the same name in the same directory.
> kobject: 'node0' ((____ptrval____)): kobject_release, parent (____ptrval____) (delayed 100)
> # pe_test_uint_arrays: ASSERTION FAILED at drivers/base/test/property-entry-test.c:123
> Expected node is not error, but is: -17
> not ok 2 - pe_test_uint_arrays
> <snip>
>
> Reported-by: Heidi Fahim <heidifahim@google.com>
> Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
> Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> Cc: Hans de Goede <hdegoede@redhat.com>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/base/swnode.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
> index 0b081dee1e95c..de8d3543e8fe3 100644
> --- a/drivers/base/swnode.c
> +++ b/drivers/base/swnode.c
> @@ -608,6 +608,13 @@ static void software_node_release(struct kobject *kobj)
> {
> struct swnode *swnode = kobj_to_swnode(kobj);
>
> + if (swnode->parent) {
> + ida_simple_remove(&swnode->parent->child_ids, swnode->id);
> + list_del(&swnode->entry);
> + } else {
> + ida_simple_remove(&swnode_root_ids, swnode->id);
> + }
> +
> if (swnode->allocated) {
> property_entries_free(swnode->node->properties);
> kfree(swnode->node);
> @@ -773,13 +780,6 @@ void fwnode_remove_software_node(struct fwnode_handle *fwnode)
> if (!swnode)
> return;
>
> - if (swnode->parent) {
> - ida_simple_remove(&swnode->parent->child_ids, swnode->id);
> - list_del(&swnode->entry);
> - } else {
> - ida_simple_remove(&swnode_root_ids, swnode->id);
> - }
> -
> kobject_put(&swnode->kobj);
> }
> EXPORT_SYMBOL_GPL(fwnode_remove_software_node);


This patch breaks tests for %pfw printk modifier added by the commit
f1ce39df508de4a4abd83da ("lib/test_printf: Add tests for %pfw printk
modifier").

Steps to reproduce:

+ build with CONFIG_TEST_PRINTF
+ boot
+ modprobe test_printf

I get the following:

[ 97.604868] test_printf: loaded.
[ 97.606153] BUG: kernel NULL pointer dereference, address: 0000000000000000
[ 97.606186] #PF: supervisor read access in kernel mode
[ 97.606206] #PF: error_code(0x0000) - not-present page
[ 97.606227] PGD 0 P4D 0
[ 97.606245] Oops: 0000 [#1] SMP PTI
[ 97.606265] CPU: 2 PID: 5125 Comm: modprobe Kdump: loaded Tainted: G E 5.7.0-rc6-default+ #5064
[ 97.606295] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-0-ga698c89-rebuilt.opensuse.org 04/01/2014
[ 97.606356] RIP: 0010:ida_free+0x76/0x140
[ 97.606376] Code: 00 00 48 c7 44 24 28 00 00 00 00 0f 88 c0 00 00 00 89 f3 e8 3c 13 60 00 48 89 e7 49 89 c5 e8 b1 fd 00 00 a8 01 48 89 c5 75 41 <4c> 0f a3 20 72 74 48 8b 3c 24 4c 89 ee e8 38 0c 60 00 89 de 48 c7
[ 97.606428] RSP: 0018:ffffad38c045ba78 EFLAGS: 00010046
[ 97.606448] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000001
[ 97.606472] RDX: 0000000000000000 RSI: ffff8dc5a6d87280 RDI: 0000000000000046
[ 97.606501] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
[ 97.606533] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
[ 97.606564] R13: 0000000000000246 R14: ffffffffc0078948 R15: ffffad38c045be88
[ 97.606600] FS: 00007f60f1834b80(0000) GS:ffff8dc5bfc00000(0000) knlGS:0000000000000000
[ 97.606638] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 97.606667] CR2: 0000000000000000 CR3: 0000000066eaa002 CR4: 0000000000360ee0
[ 97.606711] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 97.606745] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 97.606780] Call Trace:
[ 97.606874] software_node_release+0x26/0xa0
[ 97.606912] kobject_put+0xa6/0x1b0
[ 97.606945] kobject_del+0x45/0x60
[ 97.606974] kobject_put+0x8b/0x1b0
[ 97.607005] software_node_unregister_nodes+0x25/0x40
[ 97.607058] test_pointer+0xbf6/0xc1e [test_printf]
[ 97.607121] ? test_pointer+0xc1e/0xc1e [test_printf]
[ 97.607159] test_printf_init+0x368/0x100c [test_printf]
[ 97.607209] do_one_initcall+0x5d/0x2f0
[ 97.607269] do_init_module+0x5b/0x226
[ 97.607301] load_module+0x1df5/0x2380
[ 97.607373] ? ima_post_read_file+0xef/0x130
[ 97.607429] ? __do_sys_finit_module+0xe9/0x110
[ 97.607460] __do_sys_finit_module+0xe9/0x110
[ 97.607512] do_syscall_64+0x60/0x280
[ 97.607591] entry_SYSCALL_64_after_hwframe+0x49/0xb3
[ 97.607627] RIP: 0033:0x7f60f0f0a2a9
[ 97.607654] Code: 00 f3 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d bf 0b 2c 00 f7 d8 64 89 01 48
[ 97.607730] RSP: 002b:00007ffc9e4b37b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
[ 97.607769] RAX: ffffffffffffffda RBX: 0000556a7a7507f0 RCX: 00007f60f0f0a2a9
[ 97.607806] RDX: 0000000000000000 RSI: 0000556a79a11688 RDI: 0000000000000003
[ 97.607841] RBP: 0000556a79a11688 R08: 0000000000000000 R09: 0000556a7a750410
[ 97.607874] R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000040000
[ 97.607907] R13: 0000556a7a7507a0 R14: 0000000000000000 R15: 0000556a7a7507f0
[ 97.607960] Modules linked in: test_printf(E+)
[ 97.607995] CR2: 0000000000000000


I have found similar report from a test robot, see
https://lore.kernel.org/lkml/20200303002816.GW6548@shao2-debian/


I was staring into it for a while and do not understand it. The revert
makes sense. I wonder if it somehow changes the order in which
the release methods are called.

Anyway, reverting the revert makes test_printf working.

Best Regards,
Petr

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