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mmc: msm_sdcc: fix race conditions in runtime PM

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commit 386ad800716b6660d40c677b57ee4bf8e4430329 msm-3.4

What is the race condition? (NOTE: RPM stands for Runtime Power Management)

1. SDCC is in RPM_SUSPENEDED state and SDCC platform suspend gets
   triggered and then system goes into suspend.
2. During platform resume, SDCC platform resume is triggered
   which blindly sets the pending_resume flag in SDCC host structure.
3. If new MMC transfer request comes then MMC block driver calls
   mmc_claim_host() which internally calls msmsdcc_enable().
4. msmsdcc_enable() checks for following 3 conditions to be true:
	1. host->sdcc_suspended == true
	2. host->pending_resume == true
	3. pm_runtime_suspended() == false
   But as SDCC state is RPM_SUSPENDED, 3rd condition is not be satisfied
   so msmsdcc_enable() don't clear the host->pending_resume flag and simply
   calls pm_runtime_get_sync() to resume the SDCC. Once SDCC is resumed,
   host->sdcc_suspended = false, runtime_status = RPM_ACTIVE but
   host->pending_resume is still set.
5. Now after RPM idle timeout, SDCC runtime suspend gets triggered which
   calls SDCC driver's runtime suspend callback (msmsdcc_runtime_suspend).
   Note that before executing the RPM suspend calllback, SDCC RPM status
   is set to RPM_SUSPENDING.
6. As SDCC driver's runtime suspend callback gets executed, it sets the
   host->sdcc_suspended to true. But now before the RPM framework
   sets the SDCC RPM status to RPM_SUSPENDED, on other active CPU core,
   new MMC transfer reques comes in which would first call msmsdcc_enable()
   and all of the 3 conditions below is true:
	1. host->sdcc_suspended == true
	2. host->pending_resume == true
	3. pm_runtime_suspended() == false (RPM status is RPM_SUSPENDING)

   As these conditions are satisfied, msmsdcc_enable() does not call
   pm_runtime_get_sync(), instead just calls pm_runtime_get_noresume() and
   msmsdcc_runtime_resume(). This means even after execution of
   msmsdcc_enable(), SDCC RPM status is either RPM_SUSPENDING or
   RPM_SUSPENDED.
7. RPM suspend framework on 1st core sets the SDCC RPM status to
   RPM_SUSPENDED once SDCC runtime suspend callback returns.
8. Now once MMC transfer request is completed on other core, it will call
   msmsdcc_disable(). This function calls pm_runtime_put_sync() which
   returns -EAGAIN error as RPM status is already RPM_SUSPENED.
   This error gets returned to MMC layer so MMC layer thinks that
   SDCC is still enabled and skips call to msmsdcc_enable() until
   msmsdcc_disable() succeeds.
8. Note when msmsdcc_disable() returned error, RPM usage_counter was set to
   0 so next call to msmsdcc_disable() decrements RPM usage_counter to -1
   (remember msmsdcc_enable() was skipped).
9. Now new MMC request comes in and it will first call msmsdcc_enable()
   which calls pm_runtime_get_sync() and it sets the usage_counter to 0
   and blindly resumes the SDCC as it was already suspended. After this
   RPM status will be RPM_ACTIVE.
10. Once MMC request is processed, it will call smsdcc_disable() which
    calls pm_runtime_put_sync() and it decrements RPM usage counter to -1
    and skips scheduling runtime suspend callback as RPM usage counter
    is not 0. RPM status remains in RPM_ACTIVE.
11. Now onwards for every new MMC transfer requests, 9 and 10 repeats and
    SDCC always stays in RPM_ACTIVE state forever.

How is this race condition fixed?

Above race is created because host->pending_resume is remaining sticky.
Following changes are done to ensure that pending_resume gets set and
cleared at appropriate places:
1. In SDCC platform resume callback, set the host->pending_resume flag
   only if RPM status is RPM_ACTIVE.
2. Clear the pending_resume flag once msmsdcc_runtime_resume() is
   completed.
3. In msmsdcc_enable() function, if pending_resume flag is set skip calling
   pm_runtime_get_sync() instead directly call msmsdcc_runtime_resume()
   because RPM status is RPM_ACTIVE.

In addition, this patch adds WARN() messages in case of failures in
msmsdcc_enable() and msmsdcc_disable() functions to capture more details
in error conditions.

CRs-Fixed: 373338
Change-Id: I50d1bd63480c668dd2b83f01567f912661f0c606
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
This commit is contained in:
Devin Kim 2012-11-05 15:47:08 -08:00 committed by Iliyan Malchev
parent 21cfe24ba2
commit 4a31675ea0
1 changed files with 17 additions and 14 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

31
drivers/mmc/host/msm_sdcc.c
View file

@ -3291,6 +3291,9 @@ static void msmsdcc_print_rpm_info(struct msmsdcc_host *host)
{
struct device *dev = mmc_dev(host->mmc);
pr_info("%s: PM: sdcc_suspended=%d, pending_resume=%d, sdcc_suspending=%d\n",
mmc_hostname(host->mmc), host->sdcc_suspended,
host->pending_resume, host->sdcc_suspending);
pr_info("%s: RPM: runtime_status=%d, usage_count=%d,"
" is_suspended=%d, disable_depth=%d, runtime_error=%d,"
" request_pending=%d, request=%d\n",
@ -3312,8 +3315,7 @@ static int msmsdcc_enable(struct mmc_host *mmc)
if (mmc->card && mmc_card_sdio(mmc->card))
goto out;
if (host->sdcc_suspended && host->pending_resume &&
!pm_runtime_suspended(dev)) {
if (host->sdcc_suspended && host->pending_resume) {
host->pending_resume = false;
pm_runtime_get_noresume(dev);
rc = msmsdcc_runtime_resume(dev);
@ -3334,8 +3336,8 @@ static int msmsdcc_enable(struct mmc_host *mmc)
skip_get_sync:
if (rc < 0) {
pr_info("%s: %s: failed with error %d", mmc_hostname(mmc),
__func__, rc);
WARN(1, "%s: %s: failed with error %d\n", mmc_hostname(mmc),
__func__, rc);
msmsdcc_print_rpm_info(host);
return rc;
}
@ -3361,15 +3363,9 @@ static int msmsdcc_disable(struct mmc_host *mmc)
rc = pm_runtime_put_sync(mmc->parent);
/*
* Ignore -EAGAIN as that is not fatal, it means that
* either runtime usage count is non-zero or the runtime
* pm itself is disabled or not in proper state to process
* idle notification.
*/
if (rc < 0 && (rc != -EAGAIN)) {
pr_info("%s: %s: failed with error %d", mmc_hostname(mmc),
__func__, rc);
if (rc < 0) {
WARN(1, "%s: %s: failed with error %d\n", mmc_hostname(mmc),
__func__, rc);
msmsdcc_print_rpm_info(host);
return rc;
}
@ -6261,6 +6257,7 @@ msmsdcc_runtime_resume(struct device *dev)
wake_unlock(&host->sdio_suspend_wlock);
}
host->pending_resume = false;
pr_debug("%s: %s: end\n", mmc_hostname(mmc), __func__);
return 0;
}
@ -6333,7 +6330,13 @@ static int msmsdcc_pm_resume(struct device *dev)
if (mmc->card && mmc_card_sdio(mmc->card))
rc = msmsdcc_runtime_resume(dev);
else
/*
* As runtime PM is enabled before calling the device's platform resume
* callback, we use the pm_runtime_suspended API to know if SDCC is
* really runtime suspended or not and set the pending_resume flag only
* if its not runtime suspended.
*/
else if (!pm_runtime_suspended(dev))
host->pending_resume = true;
if (host->plat->status_irq) {