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Message-ID: <CAJ9a7VjoHP7myATdXVnC2w-vMBjPsJo024f8jLYRsjJ8UEXSsw@mail.gmail.com>
Date: Wed, 15 Jun 2022 12:33:07 +0100
From: Mike Leach <mike.leach@...aro.org>
To: Suzuki K Poulose <suzuki.poulose@....com>
Cc: linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org,
mathieu.poirier@...aro.org, leo.yan@...aro.org,
Joel Becker <jlbec@...lplan.org>,
Christoph Hellwig <hch@....de>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] coresight: configfs: Fix unload of configurations on
module exit
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@....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@....com>
> >> Signed-off-by: Mike Leach <mike.leach@...aro.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
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