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x86/platform/intel/iosf_mbi Rewrite locking 

There are 2 problems with the old iosf PMIC I2C bus arbritration code which
need to be addressed:

1. The lockdep code complains about a possible deadlock in the
iosf_mbi_[un]block_punit_i2c_access code:

[    6.712662] ======================================================
[    6.712673] WARNING: possible circular locking dependency detected
[    6.712685] 5.3.0-rc2+ #79 Not tainted
[    6.712692] ------------------------------------------------------
[    6.712702] kworker/0:1/7 is trying to acquire lock:
[    6.712712] 00000000df1c5681 (iosf_mbi_block_punit_i2c_access_count_mutex){+.+.}, at: iosf_mbi_unblock_punit_i2c_access+0x13/0x90
[    6.712739]
               but task is already holding lock:
[    6.712749] 0000000067cb23e7 (iosf_mbi_punit_mutex){+.+.}, at: iosf_mbi_block_punit_i2c_access+0x97/0x186
[    6.712768]
               which lock already depends on the new lock.

[    6.712780]
               the existing dependency chain (in reverse order) is:
[    6.712792]
               -> #1 (iosf_mbi_punit_mutex){+.+.}:
[    6.712808]        __mutex_lock+0xa8/0x9a0
[    6.712818]        iosf_mbi_block_punit_i2c_access+0x97/0x186
[    6.712831]        i2c_dw_acquire_lock+0x20/0x30
[    6.712841]        i2c_dw_set_reg_access+0x15/0xb0
[    6.712851]        i2c_dw_probe+0x57/0x473
[    6.712861]        dw_i2c_plat_probe+0x33e/0x640
[    6.712874]        platform_drv_probe+0x38/0x80
[    6.712884]        really_probe+0xf3/0x380
[    6.712894]        driver_probe_device+0x59/0xd0
[    6.712905]        bus_for_each_drv+0x84/0xd0
[    6.712915]        __device_attach+0xe4/0x170
[    6.712925]        bus_probe_device+0x9f/0xb0
[    6.712935]        deferred_probe_work_func+0x79/0xd0
[    6.712946]        process_one_work+0x234/0x560
[    6.712957]        worker_thread+0x50/0x3b0
[    6.712967]        kthread+0x10a/0x140
[    6.712977]        ret_from_fork+0x3a/0x50
[    6.712986]
               -> #0 (iosf_mbi_block_punit_i2c_access_count_mutex){+.+.}:
[    6.713004]        __lock_acquire+0xe07/0x1930
[    6.713015]        lock_acquire+0x9d/0x1a0
[    6.713025]        __mutex_lock+0xa8/0x9a0
[    6.713035]        iosf_mbi_unblock_punit_i2c_access+0x13/0x90
[    6.713047]        i2c_dw_set_reg_access+0x4d/0xb0
[    6.713058]        i2c_dw_probe+0x57/0x473
[    6.713068]        dw_i2c_plat_probe+0x33e/0x640
[    6.713079]        platform_drv_probe+0x38/0x80
[    6.713089]        really_probe+0xf3/0x380
[    6.713099]        driver_probe_device+0x59/0xd0
[    6.713109]        bus_for_each_drv+0x84/0xd0
[    6.713119]        __device_attach+0xe4/0x170
[    6.713129]        bus_probe_device+0x9f/0xb0
[    6.713140]        deferred_probe_work_func+0x79/0xd0
[    6.713150]        process_one_work+0x234/0x560
[    6.713160]        worker_thread+0x50/0x3b0
[    6.713170]        kthread+0x10a/0x140
[    6.713180]        ret_from_fork+0x3a/0x50
[    6.713189]
               other info that might help us debug this:

[    6.713202]  Possible unsafe locking scenario:

[    6.713212]        CPU0                    CPU1
[    6.713221]        ----                    ----
[    6.713229]   lock(iosf_mbi_punit_mutex);
[    6.713239]                                lock(iosf_mbi_block_punit_i2c_access_count_mutex);
[    6.713253]                                lock(iosf_mbi_punit_mutex);
[    6.713265]   lock(iosf_mbi_block_punit_i2c_access_count_mutex);
[    6.713276]
                *** DEADLOCK ***

In practice can never happen because only the first caller which
increments iosf_mbi_block_punit_i2c_access_count will also take
iosf_mbi_punit_mutex, that is the whole purpose of the counter, which
itself is protected by iosf_mbi_block_punit_i2c_access_count_mutex.

But there is no way to tell the lockdep code about this and we really
want to be able to run a kernel with lockdep enabled without these
warnings being triggered.

2. The lockdep warning also points out another real problem, if 2 threads
both are in a block of code protected by iosf_mbi_block_punit_i2c_access
and the first thread to acquire the block exits before the second thread
then the second thread will call mutex_unlock on iosf_mbi_punit_mutex,
but it is not the thread which took the mutex and unlocking by another
thread is not allowed.

Fix this by getting rid of the notion of holding a mutex for the entire
duration of the PMIC accesses, be it either from the PUnit side, or from an
in kernel I2C driver. In general holding a mutex after exiting a function
is a bad idea and the above problems show this case is no different.

Instead 2 counters are now used, one for PMIC accesses from the PUnit
and one for accesses from in kernel I2C code. When access is requested
now the code will wait (using a waitqueue) for the counter of the other
type of access to reach 0 and on release, if the counter reaches 0 the
wakequeue is woken.

Note that the counter approach is necessary to allow nested calls.
The main reason for this is so that a series of i2c transfers can be done
with the punit blocked from accessing the bus the whole time. This is
necessary to be able to safely read/modify/write a PMIC register without
racing with the PUNIT doing the same thing.

Allowing nested iosf_mbi_block_punit_i2c_access() calls also is desirable
from a performance pov since the whole dance necessary to block the PUnit
from accessing the PMIC I2C bus is somewhat expensive.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lkml.kernel.org/r/20190812102113.95794-1-hdegoede@redhat.com
This commit is contained in:
Hans de Goede 2019-08-12 12:21:13 +02:00 committed by Thomas Gleixner
parent d1abaeb3be
commit 00452ba9fd
1 changed files with 62 additions and 38 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

100
arch/x86/platform/intel/iosf_mbi.c
View File

@ -17,6 +17,7 @@
#include <linux/debugfs.h>
#include <linux/capability.h>
#include <linux/pm_qos.h>
#include <linux/wait.h>
#include <asm/iosf_mbi.h>
@ -201,23 +202,45 @@ EXPORT_SYMBOL(iosf_mbi_available);
#define PUNIT_SEMAPHORE_BIT BIT(0)
#define PUNIT_SEMAPHORE_ACQUIRE BIT(1)
static DEFINE_MUTEX(iosf_mbi_punit_mutex);
static DEFINE_MUTEX(iosf_mbi_block_punit_i2c_access_count_mutex);
static DEFINE_MUTEX(iosf_mbi_pmic_access_mutex);
static BLOCKING_NOTIFIER_HEAD(iosf_mbi_pmic_bus_access_notifier);
static u32 iosf_mbi_block_punit_i2c_access_count;
static DECLARE_WAIT_QUEUE_HEAD(iosf_mbi_pmic_access_waitq);
static u32 iosf_mbi_pmic_punit_access_count;
static u32 iosf_mbi_pmic_i2c_access_count;
static u32 iosf_mbi_sem_address;
static unsigned long iosf_mbi_sem_acquired;
static struct pm_qos_request iosf_mbi_pm_qos;
void iosf_mbi_punit_acquire(void)
{
mutex_lock(&iosf_mbi_punit_mutex);
/* Wait for any I2C PMIC accesses from in kernel drivers to finish. */
mutex_lock(&iosf_mbi_pmic_access_mutex);
while (iosf_mbi_pmic_i2c_access_count != 0) {
mutex_unlock(&iosf_mbi_pmic_access_mutex);
wait_event(iosf_mbi_pmic_access_waitq,
iosf_mbi_pmic_i2c_access_count == 0);
mutex_lock(&iosf_mbi_pmic_access_mutex);
}
/*
* We do not need to do anything to allow the PUNIT to safely access
* the PMIC, other then block in kernel accesses to the PMIC.
*/
iosf_mbi_pmic_punit_access_count++;
mutex_unlock(&iosf_mbi_pmic_access_mutex);
}
EXPORT_SYMBOL(iosf_mbi_punit_acquire);
void iosf_mbi_punit_release(void)
{
mutex_unlock(&iosf_mbi_punit_mutex);
bool do_wakeup;
mutex_lock(&iosf_mbi_pmic_access_mutex);
iosf_mbi_pmic_punit_access_count--;
do_wakeup = iosf_mbi_pmic_punit_access_count == 0;
mutex_unlock(&iosf_mbi_pmic_access_mutex);
if (do_wakeup)
wake_up(&iosf_mbi_pmic_access_waitq);
}
EXPORT_SYMBOL(iosf_mbi_punit_release);
@ -256,34 +279,32 @@ static void iosf_mbi_reset_semaphore(void)
* already blocked P-Unit accesses because it wants them blocked over multiple
* i2c-transfers, for e.g. read-modify-write of an I2C client register.
*
* The P-Unit accesses already being blocked is tracked through the
* iosf_mbi_block_punit_i2c_access_count variable which is protected by the
* iosf_mbi_block_punit_i2c_access_count_mutex this mutex is hold for the
* entire duration of the function.
*
* If access is not blocked yet, this function takes the following steps:
* To allow safe PMIC i2c bus accesses this function takes the following steps:
*
* 1) Some code sends request to the P-Unit which make it access the PMIC
* I2C bus. Testing has shown that the P-Unit does not check its internal
* PMIC bus semaphore for these requests. Callers of these requests call
* iosf_mbi_punit_acquire()/_release() around their P-Unit accesses, these
* functions lock/unlock the iosf_mbi_punit_mutex.
* As the first step we lock the iosf_mbi_punit_mutex, to wait for any in
* flight requests to finish and to block any new requests.
* functions increase/decrease iosf_mbi_pmic_punit_access_count, so first
* we wait for iosf_mbi_pmic_punit_access_count to become 0.
*
* 2) Some code makes such P-Unit requests from atomic contexts where it
* 2) Check iosf_mbi_pmic_i2c_access_count, if access has already
* been blocked by another caller, we only need to increment
* iosf_mbi_pmic_i2c_access_count and we can skip the other steps.
*
* 3) Some code makes such P-Unit requests from atomic contexts where it
* cannot call iosf_mbi_punit_acquire() as that may sleep.
* As the second step we call a notifier chain which allows any code
* needing P-Unit resources from atomic context to acquire them before
* we take control over the PMIC I2C bus.
*
* 3) When CPU cores enter C6 or C7 the P-Unit needs to talk to the PMIC
* 4) When CPU cores enter C6 or C7 the P-Unit needs to talk to the PMIC
* if this happens while the kernel itself is accessing the PMIC I2C bus
* the SoC hangs.
* As the third step we call pm_qos_update_request() to disallow the CPU
* to enter C6 or C7.
*
* 4) The P-Unit has a PMIC bus semaphore which we can request to stop
* 5) The P-Unit has a PMIC bus semaphore which we can request to stop
* autonomous P-Unit tasks from accessing the PMIC I2C bus while we hold it.
* As the fourth and final step we request this semaphore and wait for our
* request to be acknowledged.
@ -297,12 +318,18 @@ int iosf_mbi_block_punit_i2c_access(void)
if (WARN_ON(!mbi_pdev || !iosf_mbi_sem_address))
return -ENXIO;
mutex_lock(&iosf_mbi_block_punit_i2c_access_count_mutex);
mutex_lock(&iosf_mbi_pmic_access_mutex);
if (iosf_mbi_block_punit_i2c_access_count > 0)
while (iosf_mbi_pmic_punit_access_count != 0) {
mutex_unlock(&iosf_mbi_pmic_access_mutex);
wait_event(iosf_mbi_pmic_access_waitq,
iosf_mbi_pmic_punit_access_count == 0);
mutex_lock(&iosf_mbi_pmic_access_mutex);
}
if (iosf_mbi_pmic_i2c_access_count > 0)
goto success;
mutex_lock(&iosf_mbi_punit_mutex);
blocking_notifier_call_chain(&iosf_mbi_pmic_bus_access_notifier,
MBI_PMIC_BUS_ACCESS_BEGIN, NULL);
@ -330,10 +357,6 @@ int iosf_mbi_block_punit_i2c_access(void)
iosf_mbi_sem_acquired = jiffies;
dev_dbg(&mbi_pdev->dev, "P-Unit semaphore acquired after %ums\n",
jiffies_to_msecs(jiffies - start));
/*
* Success, keep iosf_mbi_punit_mutex locked till
* iosf_mbi_unblock_punit_i2c_access() gets called.
*/
goto success;
}
@ -344,15 +367,13 @@ int iosf_mbi_block_punit_i2c_access(void)
dev_err(&mbi_pdev->dev, "Error P-Unit semaphore timed out, resetting\n");
error:
iosf_mbi_reset_semaphore();
mutex_unlock(&iosf_mbi_punit_mutex);
if (!iosf_mbi_get_sem(&sem))
dev_err(&mbi_pdev->dev, "P-Unit semaphore: %d\n", sem);
success:
if (!WARN_ON(ret))
iosf_mbi_block_punit_i2c_access_count++;
iosf_mbi_pmic_i2c_access_count++;
mutex_unlock(&iosf_mbi_block_punit_i2c_access_count_mutex);
mutex_unlock(&iosf_mbi_pmic_access_mutex);
return ret;
}
@ -360,17 +381,20 @@ EXPORT_SYMBOL(iosf_mbi_block_punit_i2c_access);
void iosf_mbi_unblock_punit_i2c_access(void)
{
mutex_lock(&iosf_mbi_block_punit_i2c_access_count_mutex);
bool do_wakeup = false;
iosf_mbi_block_punit_i2c_access_count--;
if (iosf_mbi_block_punit_i2c_access_count == 0) {
mutex_lock(&iosf_mbi_pmic_access_mutex);
iosf_mbi_pmic_i2c_access_count--;
if (iosf_mbi_pmic_i2c_access_count == 0) {
iosf_mbi_reset_semaphore();
mutex_unlock(&iosf_mbi_punit_mutex);
dev_dbg(&mbi_pdev->dev, "punit semaphore held for %ums\n",
jiffies_to_msecs(jiffies - iosf_mbi_sem_acquired));
do_wakeup = true;
}
mutex_unlock(&iosf_mbi_pmic_access_mutex);
mutex_unlock(&iosf_mbi_block_punit_i2c_access_count_mutex);
if (do_wakeup)
wake_up(&iosf_mbi_pmic_access_waitq);
}
EXPORT_SYMBOL(iosf_mbi_unblock_punit_i2c_access);
@ -379,10 +403,10 @@ int iosf_mbi_register_pmic_bus_access_notifier(struct notifier_block *nb)
int ret;
/* Wait for the bus to go inactive before registering */
mutex_lock(&iosf_mbi_punit_mutex);
iosf_mbi_punit_acquire();
ret = blocking_notifier_chain_register(
&iosf_mbi_pmic_bus_access_notifier, nb);
mutex_unlock(&iosf_mbi_punit_mutex);
iosf_mbi_punit_release();
return ret;
}
@ -403,9 +427,9 @@ int iosf_mbi_unregister_pmic_bus_access_notifier(struct notifier_block *nb)
int ret;
/* Wait for the bus to go inactive before unregistering */
mutex_lock(&iosf_mbi_punit_mutex);
iosf_mbi_punit_acquire();
ret = iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(nb);
mutex_unlock(&iosf_mbi_punit_mutex);
iosf_mbi_punit_release();
return ret;
}
@ -413,7 +437,7 @@ EXPORT_SYMBOL(iosf_mbi_unregister_pmic_bus_access_notifier);
void iosf_mbi_assert_punit_acquired(void)
{
WARN_ON(!mutex_is_locked(&iosf_mbi_punit_mutex));
WARN_ON(iosf_mbi_pmic_punit_access_count == 0);
}
EXPORT_SYMBOL(iosf_mbi_assert_punit_acquired);