diff mbox series

interconnect: avoid memory allocation when 'icc_bw_lock' is held

Message ID 20250529-icc-bw-lockdep-v1-1-3d714b6a9374@gmail.com
State New
Headers show
Series interconnect: avoid memory allocation when 'icc_bw_lock' is held | expand

Commit Message

Gabor Juhos May 29, 2025, 2:46 p.m. UTC 
The 'icc_bw_lock' mutex is introduced in commit af42269c3523
("interconnect: Fix locking for runpm vs reclaim") in order
to decouple serialization of bw aggregation from codepaths
that require memory allocation.

However commit d30f83d278a9 ("interconnect: core: Add dynamic
id allocation support") added a devm_kasprintf() call into a
path protected by the 'icc_bw_lock' which causes this lockdep
warning (at least on the IPQ9574 platform):

    ======================================================
    WARNING: possible circular locking dependency detected
    6.15.0-next-20250529 #0 Not tainted
    ------------------------------------------------------
    swapper/0/1 is trying to acquire lock:
    ffffffc081df57d8 (icc_bw_lock){+.+.}-{4:4}, at: icc_init+0x8/0x108

    but task is already holding lock:
    ffffffc081d7db10 (fs_reclaim){+.+.}-{0:0}, at: icc_init+0x28/0x108

    which lock already depends on the new lock.

    the existing dependency chain (in reverse order) is:

    -> #1 (fs_reclaim){+.+.}-{0:0}:
           fs_reclaim_acquire+0x7c/0xb8
           slab_alloc_node.isra.0+0x48/0x188
           __kmalloc_node_track_caller_noprof+0xa4/0x2b8
           devm_kmalloc+0x5c/0x138
           devm_kvasprintf+0x6c/0xb8
           devm_kasprintf+0x50/0x68
           icc_node_add+0xbc/0x160
           icc_clk_register+0x15c/0x230
           devm_icc_clk_register+0x20/0x90
           qcom_cc_really_probe+0x320/0x338
           nss_cc_ipq9574_probe+0xac/0x1e8
           platform_probe+0x70/0xd0
           really_probe+0xdc/0x3b8
           __driver_probe_device+0x94/0x178
           driver_probe_device+0x48/0xf0
           __driver_attach+0x13c/0x208
           bus_for_each_dev+0x6c/0xb8
           driver_attach+0x2c/0x40
           bus_add_driver+0x100/0x250
           driver_register+0x68/0x138
           __platform_driver_register+0x2c/0x40
           nss_cc_ipq9574_driver_init+0x24/0x38
           do_one_initcall+0x88/0x340
           kernel_init_freeable+0x2ac/0x4f8
           kernel_init+0x28/0x1e8
           ret_from_fork+0x10/0x20

    -> #0 (icc_bw_lock){+.+.}-{4:4}:
           __lock_acquire+0x1348/0x2090
           lock_acquire+0x108/0x2d8
           icc_init+0x50/0x108
           do_one_initcall+0x88/0x340
           kernel_init_freeable+0x2ac/0x4f8
           kernel_init+0x28/0x1e8
           ret_from_fork+0x10/0x20

    other info that might help us debug this:

     Possible unsafe locking scenario:

           CPU0                    CPU1
           ----                    ----
      lock(fs_reclaim);
                                   lock(icc_bw_lock);
                                   lock(fs_reclaim);
      lock(icc_bw_lock);

     *** DEADLOCK ***

    1 lock held by swapper/0/1:
     #0: ffffffc081d7db10 (fs_reclaim){+.+.}-{0:0}, at: icc_init+0x28/0x108

    stack backtrace:
    CPU: 3 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.15.0-next-20250529 #0 NONE
    Hardware name: Qualcomm Technologies, Inc. IPQ9574/AP-AL02-C7 (DT)
    Call trace:
     show_stack+0x20/0x38 (C)
     dump_stack_lvl+0x90/0xd0
     dump_stack+0x18/0x28
     print_circular_bug+0x334/0x448
     check_noncircular+0x12c/0x140
     __lock_acquire+0x1348/0x2090
     lock_acquire+0x108/0x2d8
     icc_init+0x50/0x108
     do_one_initcall+0x88/0x340
     kernel_init_freeable+0x2ac/0x4f8
     kernel_init+0x28/0x1e8
     ret_from_fork+0x10/0x20

Move the memory allocation part of the code outside of the protected
path to eliminate the warning. Also add a note about why it is moved
to there,

Fixes: d30f83d278a9 ("interconnect: core: Add dynamic id allocation support")
Signed-off-by: Gabor Juhos <j4g8y7@gmail.com>
---
 drivers/interconnect/core.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)


---
base-commit: 5fed7fe33c2cd7104fc87b7bc699a7be892befa2
change-id: 20250529-icc-bw-lockdep-ed030d892a19

Best regards,

Comments

Gabor Juhos June 3, 2025, 9:15 a.m. UTC | #1 
Hello Bryan,

Sorry for the late reply, I missed your mail.

2025. 05. 30. 11:16 keltezéssel, Bryan O'Donoghue írta:
> On 29/05/2025 15:46, Gabor Juhos wrote:
>> The 'icc_bw_lock' mutex is introduced in commit af42269c3523
>> ("interconnect: Fix locking for runpm vs reclaim") in order
>> to decouple serialization of bw aggregation from codepaths
>> that require memory allocation.
>>
>> However commit d30f83d278a9 ("interconnect: core: Add dynamic
>> id allocation support") added a devm_kasprintf() call into a
>> path protected by the 'icc_bw_lock' which causes this lockdep
>> warning (at least on the IPQ9574 platform):
> 
> Missing a Fixes tag.

Erm, it is before my s-o-b tag.

...

>> Move the memory allocation part of the code outside of the protected
>> path to eliminate the warning. Also add a note about why it is moved
>> to there,
>>
>> Fixes: d30f83d278a9 ("interconnect: core: Add dynamic id allocation support")
>> Signed-off-by: Gabor Juhos <j4g8y7@gmail.com>
>> ---
>>   drivers/interconnect/core.c | 14 ++++++++++----
>>   1 file changed, 10 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
>> index
>> 1a41e59c77f85a811f78986e98401625f4cadfa3..acdb3b8f1e54942dbb1b71ec2b170b08ad709e6b 100644
>> --- a/drivers/interconnect/core.c
>> +++ b/drivers/interconnect/core.c
>> @@ -1023,6 +1023,16 @@ void icc_node_add(struct icc_node *node, struct
>> icc_provider *provider)
>>           return;
>>
>>       mutex_lock(&icc_lock);
>> +
>> +    if (node->id >= ICC_DYN_ID_START) {
>> +        /*
>> +         * Memory allocation must be done outside of codepaths
>> +         * protected by icc_bw_lock.
>> +         */
>> +        node->name = devm_kasprintf(provider->dev, GFP_KERNEL, "%s@%s",
>> +                        node->name, dev_name(provider->dev));
>> +    }
>> +
>>       mutex_lock(&icc_bw_lock);
>>
>>       node->provider = provider;
>> @@ -1038,10 +1048,6 @@ void icc_node_add(struct icc_node *node, struct
>> icc_provider *provider)
>>       node->avg_bw = node->init_avg;
>>       node->peak_bw = node->init_peak;
>>
>> -    if (node->id >= ICC_DYN_ID_START)
>> -        node->name = devm_kasprintf(provider->dev, GFP_KERNEL, "%s@%s",
>> -                        node->name, dev_name(provider->dev));
>> -
>>       if (node->avg_bw || node->peak_bw) {
>>           if (provider->pre_aggregate)
>>               provider->pre_aggregate(node);
>>
>> ---
>> base-commit: 5fed7fe33c2cd7104fc87b7bc699a7be892befa2
>> change-id: 20250529-icc-bw-lockdep-ed030d892a19
>>
>> Best regards,
>> -- 
>> Gabor Juhos <j4g8y7@gmail.com>
>>
>>
> 
> The locking in this code is a mess.
> 
> Which data-structures does icc_lock protect node* pointers I think and which
> data-structures does icc_bw_lock protect - "bw" data structures ?
> 
> Hmm.
> 
> Looking at this code I'm not sure at all what icc_lock was introduced to do.

Initially, only the 'icc_lock' mutex was here, and that protected 'everything'.
The 'icc_bw_lock' has been introduced later by commit af42269c3523
("interconnect: Fix locking for runpm vs reclaim") as part of the
"drm/msm+PM+icc: Make job_run() reclaim-safe" series [1].

Here is the reason copied from the original commit message:

    "For cases where icc_bw_set() can be called in callbaths that could
    deadlock against shrinker/reclaim, such as runpm resume, we need to
    decouple the icc locking.  Introduce a new icc_bw_lock for cases where
    we need to serialize bw aggregation and update to decouple that from
    paths that require memory allocation such as node/link creation/
    destruction."

> Can we not just drop it entirely ?

I'm not an expert in locking, but I doubt that we can easily drop any of the two
mutexes without reintroducing the problem fixed by the change mentioned above.

[1] https://lore.kernel.org/all/20230807171148.210181-1-robdclark@gmail.com/

Regards,
Gabor
diff mbox series

Patch

diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
index 1a41e59c77f85a811f78986e98401625f4cadfa3..acdb3b8f1e54942dbb1b71ec2b170b08ad709e6b 100644
--- a/drivers/interconnect/core.c
+++ b/drivers/interconnect/core.c
@@ -1023,6 +1023,16 @@  void icc_node_add(struct icc_node *node, struct icc_provider *provider)
 		return;
 
 	mutex_lock(&icc_lock);
+
+	if (node->id >= ICC_DYN_ID_START) {
+		/*
+		 * Memory allocation must be done outside of codepaths
+		 * protected by icc_bw_lock.
+		 */
+		node->name = devm_kasprintf(provider->dev, GFP_KERNEL, "%s@%s",
+					    node->name, dev_name(provider->dev));
+	}
+
 	mutex_lock(&icc_bw_lock);
 
 	node->provider = provider;
@@ -1038,10 +1048,6 @@  void icc_node_add(struct icc_node *node, struct icc_provider *provider)
 	node->avg_bw = node->init_avg;
 	node->peak_bw = node->init_peak;
 
-	if (node->id >= ICC_DYN_ID_START)
-		node->name = devm_kasprintf(provider->dev, GFP_KERNEL, "%s@%s",
-					    node->name, dev_name(provider->dev));
-
 	if (node->avg_bw || node->peak_bw) {
 		if (provider->pre_aggregate)
 			provider->pre_aggregate(node);