On 9 October 2013 02:48, Grant Grundler <grundler@xxxxxxxxxxxx> wrote: > Ulf, > While this patch might be correct, it's not solving the problem I > claimed and my explanation was wrong. See comments in this code > review: > https://chromium-review.googlesource.com/#/c/170880/1//COMMIT_MSG > > While I no longer see the same crash with this change in our "ToT > tree", I'm able to reproduce the original mmcqd crash on a different > kernel variant (also based on chromeos-3.4 kernel). > > I think I need to review references to mqrq_prev and mqrq_cur since > those appear to be protected by mq->thread_sem and I suspect > references are happening from dw_mmc tasklet without holding this > semaphore. > > apologies, > grant > No worries Grant. Feel free to add me on Cc if you send a patch for dw_mmc to fix the problem, maybe I can help out reviewing. Kind regards Ulf Hansson > > On Thu, Sep 26, 2013 at 12:22 PM, Grant Grundler <grundler@xxxxxxxxxxxx> wrote: >> Races between host->areq being NULL or not are resulting in mmcqd >> hung_task panics. Like this one: >> >> <3>[ 240.501202] INFO: task mmcqd/1:85 blocked for more than 120 seconds. >> <3>[ 240.501213] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >> <6>[ 240.501223] mmcqd/1 D 80528020 0 85 2 0x00000000 >> <5>[ 240.501254] [<80528020>] (__schedule+0x614/0x780) from [<80528550>] (schedule+0x94/0x98) >> <5>[ 240.501269] [<80528550>] (schedule+0x94/0x98) from [<80526270>] (schedule_timeout+0x38/0x2d0) >> <5>[ 240.501284] [<80526270>] (schedule_timeout+0x38/0x2d0) from [<805283a4>] (wait_for_common+0x164/0x1a0) >> <5>[ 240.501298] [<805283a4>] (wait_for_common+0x164/0x1a0) from [<805284b8>] (wait_for_completion+0x20/0x24) >> <5>[ 240.501313] [<805284b8>] (wait_for_completion+0x20/0x24) from [<803d7068>] (mmc_wait_for_req_done+0x2c/0x84) >> <5>[ 240.501327] [<803d7068>] (mmc_wait_for_req_done+0x2c/0x84) from [<803d81c0>] (mmc_start_req+0x60/0x120) >> <5>[ 240.501342] [<803d81c0>] (mmc_start_req+0x60/0x120) from [<803e402c>] (mmc_blk_issue_rw_rq+0xa0/0x3a8) >> <5>[ 240.501355] [<803e402c>] (mmc_blk_issue_rw_rq+0xa0/0x3a8) from [<803e4758>] (mmc_blk_issue_rq+0x424/0x478) >> <5>[ 240.501368] [<803e4758>] (mmc_blk_issue_rq+0x424/0x478) from [<803e587c>] (mmc_queue_thread+0xb0/0x118) >> <5>[ 240.501382] [<803e587c>] (mmc_queue_thread+0xb0/0x118) from [<8004d61c>] (kthread+0xa8/0xbc) >> <5>[ 240.501396] [<8004d61c>] (kthread+0xa8/0xbc) from [<8000f1c8>] (kernel_thread_exit+0x0/0x8) >> <0>[ 240.501407] Kernel panic - not syncing: hung_task: blocked tasks >> <5>[ 240.501421] [<800150a4>] (unwind_backtrace+0x0/0x114) from [<80521920>] (dump_stack+0x20/0x24) >> <5>[ 240.501434] [<80521920>] (dump_stack+0x20/0x24) from [<80521a90>] (panic+0xa8/0x1f4) >> <5>[ 240.501447] [<80521a90>] (panic+0xa8/0x1f4) from [<80086d3c>] (watchdog+0x1f4/0x25c) >> <5>[ 240.501459] [<80086d3c>] (watchdog+0x1f4/0x25c) from [<8004d61c>] (kthread+0xa8/0xbc) >> <5>[ 240.501471] [<8004d61c>] (kthread+0xa8/0xbc) from [<8000f1c8>] (kernel_thread_exit+0x0/0x8) >> >> I was able to reproduce the mmcqd "hung task" timeout consistently >> with this fio command line on an Exynos5250 system with Toshiba HS200 >> eMMC running in HS200 mode: >> fio --name=short_randwrite --size=2G --time_based --runtime=3m \ >> --readwrite=randwrite --numjobs=2 --bs=4k --norandommap \ >> --ioengine=psync --direct=0 --filename=/dev/mmcblk0p5 >> >> I believe the key parameters are "--numjobs=2" (or more) and "randwrite" >> workload. Then the completions are happening around the same time as >> mmc_start_req() is referencing and/or updating host->areq. >> >> I was NOT able to consistently reproduce the problem on a similar >> Exynos 5250 system which had "engineering samples" of Samsung HS200 >> capable eMMC installed. Just my clue that the timing is different >> (and the fio performance numbers are different too). >> >> Signed-off-by: Grant Grundler <grundler@xxxxxxxxxxxx> >> --- >> drivers/mmc/core/core.c | 34 +++++++++++++++++++++++----------- >> 1 file changed, 23 insertions(+), 11 deletions(-) >> >> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c >> index 36cfe91..e5a9599 100644 >> --- a/drivers/mmc/core/core.c >> +++ b/drivers/mmc/core/core.c >> @@ -529,29 +529,40 @@ struct mmc_async_req *mmc_start_req(struct mmc_host *host, >> { >> int saved_err = 0; >> int start_err = 0; >> - struct mmc_async_req *saved_areq = host->areq; >> + struct mmc_async_req *saved_areq; >> + unsigned long flags; >> >> - if (!saved_areq && !areq) >> - /* Nothing to do...some code is polling. */ >> + spin_lock_irqsave(&host->lock, flags); >> + saved_areq = host->areq; >> + if (!saved_areq && !areq) { >> + /* Nothing? Code is racing to harvest a completion. */ >> + spin_unlock_irqrestore(&host->lock, flags); >> goto set_error; >> + } >> >> /* Prepare a new request */ >> if (areq) >> mmc_pre_req(host, areq->mrq, !saved_areq); >> >> if (saved_areq) { >> + /* This thread owns this IO (saved_areq) for now. */ >> + host->areq = NULL; >> + spin_unlock_irqrestore(&host->lock, flags); >> + >> saved_err = mmc_wait_for_data_req_done(host, saved_areq->mrq, areq); >> if (saved_err == MMC_BLK_NEW_REQUEST) { >> - /* >> - * The previous request was not completed, >> - * nothing to return >> - */ >> + spin_lock_irqsave(&host->lock, flags); >> + BUG_ON(host->areq != NULL); >> + >> + /* Not completed. Don't report it. */ >> + host->areq = saved_areq; >> saved_areq = NULL; >> + saved_err = 0; >> + spin_unlock_irqrestore(&host->lock, flags); >> goto set_error; >> } >> - /* >> - * Check BKOPS urgency for each R1 response >> - */ >> + >> + /* Check BKOPS urgency for each R1 response */ >> if (host->card && mmc_card_mmc(host->card) && >> ((mmc_resp_type(saved_areq->mrq->cmd) == MMC_RSP_R1) || >> (mmc_resp_type(saved_areq->mrq->cmd) == MMC_RSP_R1B)) && >> @@ -562,11 +573,12 @@ struct mmc_async_req *mmc_start_req(struct mmc_host *host, >> /* Don't start something new if previous one failed. */ >> if (!saved_err && areq) { >> start_err = __mmc_start_data_req(host, areq->mrq); >> + >> /* Cancel a prepared request if it was not started. */ >> if (start_err) { >> mmc_post_req(host, areq->mrq, -EINVAL); >> host->areq = NULL; >> - } else >> + } else >> host->areq = areq; >> } >> >> -- >> 1.8.4 >> -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
