Messages in this thread | | | From | Mike Leach <> | Date | Thu, 16 Jun 2022 09:10:45 +0100 | Subject | Re: [PATCH v2] coresight: configfs: Fix unload of configurations on module exit |
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On Wed, 15 Jun 2022 at 12:33, Mike Leach <mike.leach@linaro.org> wrote: > > 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? >
Hi Suzuki,
Thinking about it - option b) above seems to make the most sense so I'll do that.
Mike
> 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 been > > >> unloaded prior > > >> + * to the coresight module unload. Therefore that module > > >> has 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) > > > > > > > > -- > Mike Leach > Principal Engineer, ARM Ltd. > Manchester Design Centre. UK
-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK
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