Re: [PATCH v2] coresight: configfs: Fix unload of configurations on module exit

From: Mike Leach
Date: Thu Jun 16 2022 - 04:11:06 EST

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On Wed, 15 Jun 2022 at 12:33, Mike Leach <mike.leach@xxxxxxxxxx> 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@xxxxxxx> 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@xxxxxxx>
> > >> Signed-off-by: Mike Leach <mike.leach@xxxxxxxxxx>
> > >> ---
> > >>
> > >> 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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