Hi Suzuki,
I found something similar when I was testing v4 of the configfs load set with lockdep enabled. (Mathieu reviewed v3 of this a little while ago).
Firstly, some of this goes away if you update configfs to enhance the lockdep nest lock depth mapping on the (&p->frag_sem) nested locking elements in a similar way to which other nested semaphores in configfs have. (I have a patch - see below).
I initially noted issues related to the new 'load' & 'unload' files in my case, but the underlying issue can occur for any configfs file that calls back into the main configuration handling call and locks the main cscfg_mutex, which protects the lists of configuration and feature data.
In the v4 set I redesigned the locking code so that the cscfg_mutex is never held while calling configfs calls that manipulate the file system (register / unregister subsystem, register / unregister group) are called.
I was intending to retest all this on 5.19-rc2 when I hit the boot issue we discussed earlier. I was also going to test if the configfs lockdep patch was strictly necessary after the re-design.
So we have a choice here: a) absorb this small fix patch into the larger v4 configfs load set - and fix everything as part of that update. b) move some of the locking re-design into the fix patchset, and submit separately and before the v4 configfs load set.
Which do you prefer?
Regards
Mike
On Wed, 15 Jun 2022 at 10:24, Suzuki K Poulose suzuki.poulose@arm.com wrote:
Cc: configfs folks.
Hi Mike
On 14/06/2022 23:00, Suzuki K Poulose wrote:
Hi Mike,
Thanks for fixing this. Except for a minor nit, the patch looks good to me.
Spoke too soon. I am able to reproduce the original problem with this patch applied. Here is what I did :
# Load the coresight_etm4x module
$ modprobe coresight_etm4x
# enable autofdo configuration $ echo 1 > /sys/kernel/config/cs-syscfg/configurations/autofdo/enable
# Unload the coresight_etm4x module $ rmmod coresight_etm4x $ lsmod Module Size Used by coresight 77824 0 $ cat /sys/kernel/config/cs-syscfg/configurations/autofdo/enable 1
# Now unload the coresight module, this triggers the splat. $ rmmod coresight
[ 202.455667] cscfg: unloading preloaded configurations [ 202.455689] ======================================================
[ 202.455691] WARNING: possible circular locking dependency detected [ 202.455695] 5.19.0-rc2+ #53 Tainted: G T [ 202.455700] ------------------------------------------------------ [ 202.455702] rmmod/454 is trying to acquire lock: [ 202.455707] ffff00080363f580 (&p->frag_sem){++++}-{4:4}, at: configfs_unregister_group+0x4c/0x190 [ 202.455733] but task is already holding lock: [ 202.455735] ffff8000012e4b98 (cscfg_mutex){+.+.}-{4:4}, at: cscfg_clear_device+0x34/0xfc [coresight] [ 202.455777] which lock already depends on the new lock.
[ 202.455779] the existing dependency chain (in reverse order) is: [ 202.455781] -> #1 (cscfg_mutex){+.+.}-{4:4}: [ 202.455791] lock_acquire+0x68/0x8c [ 202.455801] __mutex_lock+0xa0/0x464 [ 202.455811] mutex_lock_nested+0x44/0x70 [ 202.455819] cscfg_config_sysfs_activate+0x3c/0xec [coresight] [ 202.455846] cscfg_cfg_enable_store+0x84/0xcc [coresight] [ 202.455872] configfs_write_iter+0xd4/0x130 [ 202.455878] new_sync_write+0xdc/0x160 [ 202.455885] vfs_write+0x1c8/0x210 [ 202.455892] ksys_write+0x74/0x100 [ 202.455897] __arm64_sys_write+0x28/0x34 [ 202.455904] invoke_syscall+0x50/0x120 [ 202.455913] el0_svc_common.constprop.0+0x68/0x124 [ 202.455921] do_el0_svc+0x38/0xcc [ 202.455928] el0_svc+0x58/0x100 [ 202.455933] el0t_64_sync_handler+0xf4/0x100 [ 202.455938] el0t_64_sync+0x18c/0x190 [ 202.455944] -> #0 (&p->frag_sem){++++}-{4:4}: [ 202.455954] __lock_acquire+0x11f4/0x1ddc [ 202.455961] lock_acquire.part.0+0xe4/0x220 [ 202.455967] lock_acquire+0x68/0x8c [ 202.455973] down_write+0x78/0x164 [ 202.455980] configfs_unregister_group+0x4c/0x190 [ 202.455985] cscfg_configfs_del_config+0x2c/0x40 [coresight] [ 202.456011] cscfg_unload_owned_cfgs_feats+0x1d0/0x2c0 [coresight] [ 202.456036] cscfg_clear_device+0xec/0xfc [coresight] [ 202.456060] cscfg_exit+0x1c/0x90 [coresight] [ 202.456085] coresight_exit+0x10/0xd80 [coresight] [ 202.456109] __arm64_sys_delete_module+0x19c/0x250 [ 202.456115] invoke_syscall+0x50/0x120 [ 202.456122] el0_svc_common.constprop.0+0x68/0x124 [ 202.456130] do_el0_svc+0x38/0xcc [ 202.456138] el0_svc+0x58/0x100 [ 202.456142] el0t_64_sync_handler+0xf4/0x100 [ 202.456148] el0t_64_sync+0x18c/0x190 [ 202.456152] other info that might help us debug this:
[ 202.456154] Possible unsafe locking scenario:
[ 202.456156] CPU0 CPU1 [ 202.456158] ---- ---- [ 202.456159] lock(cscfg_mutex); [ 202.456164] lock(&p->frag_sem); [ 202.456169] lock(cscfg_mutex); [ 202.456173] lock(&p->frag_sem); [ 202.456177] *** DEADLOCK ***
[ 202.456178] 1 lock held by rmmod/454: [ 202.456183] #0: ffff8000012e4b98 (cscfg_mutex){+.+.}-{4:4}, at: cscfg_clear_device+0x34/0xfc [coresight] [ 202.456219] stack backtrace: [ 202.456222] CPU: 1 PID: 454 Comm: rmmod Tainted: G T 5.19.0-rc2+ #53 [ 202.456230] Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Feb 1 2019 [ 202.456234] Call trace: [ 202.456236] dump_backtrace.part.0+0xd8/0xe4 [ 202.456243] show_stack+0x24/0x80 [ 202.456248] dump_stack_lvl+0x8c/0xb8 [ 202.456257] dump_stack+0x18/0x34 [ 202.456264] print_circular_bug+0x1f8/0x200 [ 202.456271] check_noncircular+0x130/0x144 [ 202.456277] __lock_acquire+0x11f4/0x1ddc [ 202.456284] lock_acquire.part.0+0xe4/0x220 [ 202.456290] lock_acquire+0x68/0x8c [ 202.456295] down_write+0x78/0x164 [ 202.456302] configfs_unregister_group+0x4c/0x190 [ 202.456308] cscfg_configfs_del_config+0x2c/0x40 [coresight] [ 202.456333] cscfg_unload_owned_cfgs_feats+0x1d0/0x2c0 [coresight] [ 202.456357] cscfg_clear_device+0xec/0xfc [coresight] [ 202.456381] cscfg_exit+0x1c/0x90 [coresight] [ 202.456405] coresight_exit+0x10/0xd80 [coresight] [ 202.456429] __arm64_sys_delete_module+0x19c/0x250 [ 202.456435] invoke_syscall+0x50/0x120 [ 202.456442] el0_svc_common.constprop.0+0x68/0x124 [ 202.456450] do_el0_svc+0x38/0xcc [ 202.456458] el0_svc+0x58/0x100 [ 202.456462] el0t_64_sync_handler+0xf4/0x100 [ 202.456468] el0t_64_sync+0x18c/0x190
Suzuki
On 06/06/2022 16:26, Mike Leach wrote:
Any loaded configurations must be correctly unloaded on coresight module exit, or issues can arise with nested locking in the configfs directory code if built with CONFIG_LOCKDEP.
Prior to this patch, the preloaded configuration configfs directory entries were being unloaded by the recursive code in configfs_unregister_subsystem().
However, when built with CONFIG_LOCKDEP, this caused a nested lock warning, which was not mitigated by the LOCKDEP dependent code in fs/configfs/dir.c designed to prevent this, due to the different directory levels for the root of the directory being removed.
As the preloaded (and all other) configurations are registered after configfs_register_subsystem(), we now explicitly unload them before the call to configfs_unregister_subsystem().
The new routine cscfg_unload_cfgs_on_exit() iterates through the load owner list to unload any remaining configurations that were not unloaded by the user before the module exits. This covers both the CSCFG_OWNER_PRELOAD and CSCFG_OWNER_MODULE owner types, and will be extended to cover future load owner types for CoreSight configurations.
Applies to coresight/next
Fixes: eb2ec49606c2 ("coresight: syscfg: Update load API for config loadable modules") Reported-by: Suzuki Poulose suzuki.poulose@arm.com Signed-off-by: Mike Leach mike.leach@linaro.org
Changes since v1: Altered ordering of init of cscfg_mgr to ensure lists valid for potential exit path on error.
.../hwtracing/coresight/coresight-syscfg.c | 72 ++++++++++++++++--- 1 file changed, 61 insertions(+), 11 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c index 11850fd8c3b5..050a32f7e439 100644 --- a/drivers/hwtracing/coresight/coresight-syscfg.c +++ b/drivers/hwtracing/coresight/coresight-syscfg.c @@ -1042,6 +1042,13 @@ static int cscfg_create_device(void) if (!cscfg_mgr) goto create_dev_exit_unlock;
- /* initialise the cscfg_mgr structure */
- INIT_LIST_HEAD(&cscfg_mgr->csdev_desc_list);
- INIT_LIST_HEAD(&cscfg_mgr->feat_desc_list);
- INIT_LIST_HEAD(&cscfg_mgr->config_desc_list);
- INIT_LIST_HEAD(&cscfg_mgr->load_order_list);
- atomic_set(&cscfg_mgr->sys_active_cnt, 0);
/* setup the device */ dev = cscfg_device(); dev->release = cscfg_dev_release;@@ -1056,14 +1063,61 @@ static int cscfg_create_device(void) return err; } -static void cscfg_clear_device(void) +/*
- Loading and unloading is generally on user discretion.
- If exiting due to coresight module unload, we need to unload any
configurations that remain,
- before we unregister the configfs intrastructure.
- Do this by walking the load_owner list and taking appropriate
action, depending on the load
- owner type.
- called with the cscfg_mutex held
- */
+#define LOADABLE_MOD_ERR "cscfg: ERROR - a loadable module failed to unload configs on exit\n"
minor nit: Could we skip this ?
+static void cscfg_unload_cfgs_on_exit(void) {
- struct cscfg_config_desc *cfg_desc;
- struct cscfg_load_owner_info *owner_info = NULL;
- mutex_lock(&cscfg_mutex);
- list_for_each_entry(cfg_desc, &cscfg_mgr->config_desc_list, item) {
etm_perf_del_symlink_cscfg(cfg_desc);
- while (!list_empty(&cscfg_mgr->load_order_list)) {
/* remove in reverse order of loading */owner_info = list_last_entry(&cscfg_mgr->load_order_list,struct cscfg_load_owner_info, item);/* action according to type */switch (owner_info->type) {case CSCFG_OWNER_PRELOAD:/** preloaded descriptors are statically allocated in* this module - just need to unload dynamic items from* csdev lists, and remove from configfs directories.*/pr_info("cscfg: unloading preloaded configurations\n");cscfg_unload_owned_cfgs_feats(owner_info);break;case CSCFG_OWNER_MODULE:/** this is an error - the loadable module must have beenunloaded prior
* to the coresight module unload. Therefore that modulehas not
* correctly unloaded configs in its own exit code.* Nothing to do other than emit an error string.*/pr_err(LOADABLE_MOD_ERR);Instead : pr_err("cscfg: ERROR - a loadable module failed" " to unload configs on exit\n");
Otherwise, I can confirm that the patch fixes the reported problem.
break;}/* remove from load order list */list_del(&owner_info->item); }+}
+static void cscfg_clear_device(void) +{
- mutex_lock(&cscfg_mutex);
- cscfg_unload_cfgs_on_exit(); cscfg_configfs_release(cscfg_mgr); device_unregister(cscfg_device()); mutex_unlock(&cscfg_mutex);
@@ -1074,20 +1128,16 @@ int __init cscfg_init(void) { int err = 0;
- /* create the device and init cscfg_mgr */ err = cscfg_create_device(); if (err) return err;
- /* initialise configfs subsystem */ err = cscfg_configfs_init(cscfg_mgr); if (err) goto exit_err;
- INIT_LIST_HEAD(&cscfg_mgr->csdev_desc_list);
- INIT_LIST_HEAD(&cscfg_mgr->feat_desc_list);
- INIT_LIST_HEAD(&cscfg_mgr->config_desc_list);
- INIT_LIST_HEAD(&cscfg_mgr->load_order_list);
- atomic_set(&cscfg_mgr->sys_active_cnt, 0);
/* preload built-in configurations */ err = cscfg_preload(THIS_MODULE); if (err)