Message-ID: <CAPDyKFoF7jz-mbsY8kPUGca5civFKRRyPpHbRkj9P=xevRRfbA@mail.gmail.com>
Date:   Wed, 20 Jan 2021 16:06:13 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Bhaskara Budiredla <bbudiredla@...vell.com>,
        Kees Cook <keescook@...omium.org>
Cc:     Colin Cross <ccross@...roid.com>, Tony Luck <tony.luck@...el.com>,
        Sunil Kovvuri Goutham <sgoutham@...vell.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v5 1/2] mmc: Support kmsg dumper based on pstore/blk

+ linux-block, Jens, Christoph

On Wed, 20 Jan 2021 at 13:11, Bhaskara Budiredla <bbudiredla@...vell.com> wrote:
>
> This patch introduces to mmcpstore. The functioning of mmcpstore
> is similar to mtdpstore. mmcpstore works on FTL based flash devices
> whereas mtdpstore works on raw flash devices. When the system crashes,
> mmcpstore stores the kmsg panic and oops logs to a user specified
> MMC device.
>
> It collects the details about the host MMC device through pstore/blk
> "blkdev" parameter. The user can specify the MMC device in many ways
> by checking in Documentation/admin-guide/pstore-blk.rst.
>
> The individual mmc host drivers have to define suitable polling and
> cleanup subroutines to write kmsg panic/oops logs through mmcpstore.
> These new host operations are needed as pstore panic write runs with
> interrupts disabled.

Okay, let me again try to clarify on how I see this to move this forward.

1)
In my opinion, pstore shouldn't be using callbacks for *regular* I/O
read/writes. It's upside-down of how the storage stack is designed to
work.

Instead, pstore should be implemented as a regular filesystem, that
can be mounted on top of a regular block device partition. In this
way, the lower layer block device drivers (as mmc), don't need special
support for pstore, the regular I/O block read/write path will just
work as is.

2)
When it comes to supporting *panic* writes for pstore, things become a
bit more complicated. For sure some adaptations are needed in each
block device driver to support this.

However, the current method means relying on the lower level block
device driver to figure out the pstore partition. Based on that, it
should then register itself for pstore support and hook up callbacks
for the corresponding block device driver instance, at least that is
what it looks like to me. Again, I think this is upside-down from the
storage stack perspective. The partition to use for pstore, should be
based upon its file system mount point.

Furthermore, I think the responsibility for lower layer block device
drivers should instead be to just "register/announce" themselves as
capable of supporting "panic writes", if they can. Exactly how to best
do this, probably needs to be discussed further with the block device
people, I think. I have looped in Jens and Christoph, perhaps they can
share their opinion in this.

That said, it looks to me that pstore needs more work before it's
ready to be adopted for generic support in block device drivers.

Kind regards
Uffe

>
> Signed-off-by: Bhaskara Budiredla <bbudiredla@...vell.com>
> ---
>  drivers/mmc/core/Kconfig     |  14 ++-
>  drivers/mmc/core/Makefile    |   1 +
>  drivers/mmc/core/block.c     |  19 +++
>  drivers/mmc/core/block.h     |   9 ++
>  drivers/mmc/core/core.c      |  44 +++++++
>  drivers/mmc/core/mmcpstore.c | 227 +++++++++++++++++++++++++++++++++++
>  include/linux/mmc/core.h     |   5 +
>  include/linux/mmc/host.h     |  12 ++
>  8 files changed, 330 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/mmc/core/mmcpstore.c
>
> diff --git a/drivers/mmc/core/Kconfig b/drivers/mmc/core/Kconfig
> index c12fe13e4b14..4c651da4f2d2 100644
> --- a/drivers/mmc/core/Kconfig
> +++ b/drivers/mmc/core/Kconfig
> @@ -34,9 +34,22 @@ config PWRSEQ_SIMPLE
>           This driver can also be built as a module. If so, the module
>           will be called pwrseq_simple.
>
> +config MMC_PSTORE_BACKEND
> +       bool "Log panic/oops to a MMC buffer"
> +       depends on MMC_BLOCK
> +       help
> +         This option will let you create platform backend to store kmsg
> +         crash dumps to a user specified MMC device. This is primarily
> +         based on pstore/blk.
> +
> +config MMC_PSTORE
> +       tristate
> +       select PSTORE_BLK
> +
>  config MMC_BLOCK
>         tristate "MMC block device driver"
>         depends on BLOCK
> +       select MMC_PSTORE if MMC_PSTORE_BACKEND=y
>         default y
>         help
>           Say Y here to enable the MMC block device driver support.
> @@ -80,4 +93,3 @@ config MMC_TEST
>
>           This driver is only of interest to those developing or
>           testing a host driver. Most people should say N here.
> -
> diff --git a/drivers/mmc/core/Makefile b/drivers/mmc/core/Makefile
> index 95ffe008ebdf..7cb9a3af4827 100644
> --- a/drivers/mmc/core/Makefile
> +++ b/drivers/mmc/core/Makefile
> @@ -16,5 +16,6 @@ obj-$(CONFIG_PWRSEQ_EMMC)     += pwrseq_emmc.o
>  mmc_core-$(CONFIG_DEBUG_FS)    += debugfs.o
>  obj-$(CONFIG_MMC_BLOCK)                += mmc_block.o
>  mmc_block-objs                 := block.o queue.o
> +mmc_block-$(CONFIG_MMC_PSTORE) += mmcpstore.o
>  obj-$(CONFIG_MMC_TEST)         += mmc_test.o
>  obj-$(CONFIG_SDIO_UART)                += sdio_uart.o
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index 42e27a298218..6592722cd7b2 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -2870,6 +2870,21 @@ static void mmc_blk_remove_debugfs(struct mmc_card *card,
>
>  #endif /* CONFIG_DEBUG_FS */
>
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +sector_t mmc_blk_get_part(struct mmc_card *card, int part_num, sector_t *size)
> +{
> +       struct mmc_blk_data *md = dev_get_drvdata(&card->dev);
> +       struct gendisk *disk = md->disk;
> +       struct disk_part_tbl *part_tbl = disk->part_tbl;
> +
> +       if (part_num < 0 || part_num >= part_tbl->len)
> +               return 0;
> +
> +       *size = part_tbl->part[part_num]->nr_sects << SECTOR_SHIFT;
> +       return part_tbl->part[part_num]->start_sect;
> +}
> +#endif
> +
>  static int mmc_blk_probe(struct mmc_card *card)
>  {
>         struct mmc_blk_data *md, *part_md;
> @@ -2913,6 +2928,9 @@ static int mmc_blk_probe(struct mmc_card *card)
>                         goto out;
>         }
>
> +       if (mmc_card_mmc(card) || mmc_card_sd(card))
> +               mmcpstore_card_set(card, md->disk->disk_name);
> +
>         /* Add two debugfs entries */
>         mmc_blk_add_debugfs(card, md);
>
> @@ -3060,6 +3078,7 @@ static void __exit mmc_blk_exit(void)
>         unregister_blkdev(MMC_BLOCK_MAJOR, "mmc");
>         unregister_chrdev_region(mmc_rpmb_devt, MAX_DEVICES);
>         bus_unregister(&mmc_rpmb_bus_type);
> +       unregister_mmcpstore();
>  }
>
>  module_init(mmc_blk_init);
> diff --git a/drivers/mmc/core/block.h b/drivers/mmc/core/block.h
> index 31153f656f41..2a4ee5568194 100644
> --- a/drivers/mmc/core/block.h
> +++ b/drivers/mmc/core/block.h
> @@ -16,5 +16,14 @@ void mmc_blk_mq_recovery(struct mmc_queue *mq);
>  struct work_struct;
>
>  void mmc_blk_mq_complete_work(struct work_struct *work);
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +sector_t mmc_blk_get_part(struct mmc_card *card, int part_num, sector_t *size);
> +void mmcpstore_card_set(struct mmc_card *card, const char *disk_name);
> +void unregister_mmcpstore(void);
> +#else
> +static inline void mmcpstore_card_set(struct mmc_card *card,
> +                                       const char *disk_name) {}
> +static inline void unregister_mmcpstore(void) {}
> +#endif
>
>  #endif
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 19f1ee57fb34..7ad7ff1cab8c 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -569,6 +569,30 @@ int mmc_cqe_recovery(struct mmc_host *host)
>  }
>  EXPORT_SYMBOL(mmc_cqe_recovery);
>
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +/**
> + *     mmc_wait_for_pstore_req - initiate a blocking mmc request
> + *     @host: MMC host to start command
> + *     @mrq: MMC request to start
> + *
> + *     Start a blocking MMC request for a host and wait for the request
> + *     to complete that is based on polling and timeout.
> + */
> +void mmc_wait_for_pstore_req(struct mmc_host *host, struct mmc_request *mrq)
> +{
> +       unsigned int timeout;
> +
> +       host->ops->req_cleanup_pending(host);
> +       mmc_start_request(host, mrq);
> +
> +       if (mrq->data) {
> +               timeout = mrq->data->timeout_ns / NSEC_PER_MSEC;
> +               host->ops->req_completion_poll(host, timeout);
> +       }
> +}
> +EXPORT_SYMBOL(mmc_wait_for_pstore_req);
> +#endif
> +
>  /**
>   *     mmc_is_req_done - Determine if a 'cap_cmd_during_tfr' request is done
>   *     @host: MMC host
> @@ -817,6 +841,26 @@ int __mmc_claim_host(struct mmc_host *host, struct mmc_ctx *ctx,
>  }
>  EXPORT_SYMBOL(__mmc_claim_host);
>
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +/**
> + *     mmc_claim_host_async - claim host in atomic context
> + *     @host: mmc host to claim
> + *
> + *     This routine may be called in panic/oops scenarios.
> + *     Return zero with host claim success, else busy status.
> + */
> +int mmc_claim_host_async(struct mmc_host *host)
> +{
> +       if (!host->claimed && pm_runtime_active(mmc_dev(host))) {
> +               host->claimed = 1;
> +               return 0;
> +       }
> +
> +       return -EBUSY;
> +}
> +EXPORT_SYMBOL(mmc_claim_host_async);
> +#endif
> +
>  /**
>   *     mmc_release_host - release a host
>   *     @host: mmc host to release
> diff --git a/drivers/mmc/core/mmcpstore.c b/drivers/mmc/core/mmcpstore.c
> new file mode 100644
> index 000000000000..f783ea215f18
> --- /dev/null
> +++ b/drivers/mmc/core/mmcpstore.c
> @@ -0,0 +1,227 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * MMC pstore support based on pstore/blk
> + *
> + * Copyright (c) 2020 Marvell.
> + * Author: Bhaskara Budiredla <bbudiredla@...vell.com>
> + */
> +
> +#define pr_fmt(fmt) "mmcpstore: " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/pstore_blk.h>
> +#include <linux/blkdev.h>
> +#include <linux/mount.h>
> +#include <linux/slab.h>
> +#include <linux/mmc/mmc.h>
> +#include <linux/mmc/host.h>
> +#include <linux/mmc/card.h>
> +#include <linux/scatterlist.h>
> +#include "block.h"
> +#include "card.h"
> +#include "core.h"
> +
> +static struct mmcpstore_context {
> +       char dev_name[BDEVNAME_SIZE];
> +       int partno;
> +       sector_t start_sect;
> +       sector_t size;
> +       struct pstore_blk_config conf;
> +       struct pstore_blk_info info;
> +
> +       struct mmc_card *card;
> +       struct mmc_request *mrq;
> +} oops_cxt;
> +
> +static void mmc_prep_req(struct mmc_request *mrq,
> +               unsigned int sect_offset, unsigned int nsects,
> +               struct scatterlist *sg, u32 opcode, unsigned int flags)
> +{
> +       mrq->cmd->opcode = opcode;
> +       mrq->cmd->arg = sect_offset;
> +       mrq->cmd->flags = MMC_RSP_R1 | MMC_CMD_ADTC;
> +
> +       if (nsects == 1) {
> +               mrq->stop = NULL;
> +       } else {
> +               mrq->stop->opcode = MMC_STOP_TRANSMISSION;
> +               mrq->stop->arg = 0;
> +               mrq->stop->flags = MMC_RSP_R1B | MMC_CMD_AC;
> +       }
> +
> +       mrq->data->blksz = SECTOR_SIZE;
> +       mrq->data->blocks = nsects;
> +       mrq->data->flags = flags;
> +       mrq->data->sg = sg;
> +       mrq->data->sg_len = 1;
> +}
> +
> +static int mmcpstore_panic_write_req(const char *buf,
> +               unsigned int nsects, unsigned int sect_offset)
> +{
> +       struct mmcpstore_context *cxt = &oops_cxt;
> +       struct mmc_request *mrq = cxt->mrq;
> +       struct mmc_card *card = cxt->card;
> +       struct mmc_host *host = card->host;
> +       struct scatterlist sg;
> +       u32 opcode;
> +       int ret;
> +
> +       opcode = (nsects > 1) ? MMC_WRITE_MULTIPLE_BLOCK : MMC_WRITE_BLOCK;
> +       mmc_prep_req(mrq, sect_offset, nsects, &sg, opcode, MMC_DATA_WRITE);
> +       sg_init_one(&sg, buf, (nsects << SECTOR_SHIFT));
> +       mmc_set_data_timeout(mrq->data, cxt->card);
> +
> +       ret = mmc_claim_host_async(host);
> +       if (ret)
> +               return ret;
> +
> +       mmc_wait_for_pstore_req(host, mrq);
> +       return 0;
> +}
> +
> +static int mmcpstore_panic_write(const char *buf, sector_t off, sector_t sects)
> +{
> +       struct mmcpstore_context *cxt = &oops_cxt;
> +       int ret;
> +
> +       ret = mmcpstore_panic_write_req(buf, sects, cxt->start_sect + off);
> +       if (ret)
> +               return ret;
> +
> +       return 0;
> +}
> +
> +static struct block_device *mmcpstore_open_backend(const char *device)
> +{
> +       struct block_device *bdev;
> +       dev_t devt;
> +
> +       bdev = blkdev_get_by_path(device, FMODE_READ, NULL);
> +       if (IS_ERR(bdev)) {
> +               devt = name_to_dev_t(device);
> +               if (devt == 0)
> +                       return ERR_PTR(-ENODEV);
> +
> +               bdev = blkdev_get_by_dev(devt, FMODE_READ, NULL);
> +               if (IS_ERR(bdev))
> +                       return bdev;
> +       }
> +
> +       return bdev;
> +}
> +
> +static void mmcpstore_close_backend(struct block_device *bdev)
> +{
> +       if (!bdev)
> +               return;
> +       blkdev_put(bdev, FMODE_READ);
> +}
> +
> +void mmcpstore_card_set(struct mmc_card *card, const char *disk_name)
> +{
> +       struct mmcpstore_context *cxt = &oops_cxt;
> +       struct pstore_blk_config *conf = &cxt->conf;
> +       struct pstore_blk_info *info = &cxt->info;
> +       struct block_device *bdev;
> +       struct mmc_command *stop;
> +       struct mmc_command *cmd;
> +       struct mmc_request *mrq;
> +       struct mmc_data *data;
> +       int ret;
> +
> +       ret = pstore_blk_get_config(conf);
> +       if (!conf->device[0]) {
> +               pr_debug("psblk backend is empty\n");
> +               return;
> +       }
> +
> +       /* Multiple backend devices not allowed */
> +       if (cxt->dev_name[0])
> +               return;
> +
> +       bdev =  mmcpstore_open_backend(conf->device);
> +       if (IS_ERR(bdev)) {
> +               pr_err("%s failed to open with %ld\n",
> +                               conf->device, PTR_ERR(bdev));
> +               return;
> +       }
> +
> +       bdevname(bdev, cxt->dev_name);
> +       cxt->partno = bdev->bd_part->partno;
> +       mmcpstore_close_backend(bdev);
> +
> +       if (strncmp(cxt->dev_name, disk_name, strlen(disk_name)))
> +               return;
> +
> +       cxt->start_sect = mmc_blk_get_part(card, cxt->partno, &cxt->size);
> +       if (!cxt->start_sect) {
> +               pr_err("Non-existent partition %d selected\n", cxt->partno);
> +               return;
> +       }
> +
> +       /* Check for host mmc panic write polling function definitions */
> +       if (!card->host->ops->req_cleanup_pending ||
> +                       !card->host->ops->req_completion_poll)
> +               return;
> +
> +       cxt->card = card;
> +
> +       mrq = kzalloc(sizeof(struct mmc_request), GFP_KERNEL);
> +       if (!mrq)
> +               goto out;
> +
> +       cmd = kzalloc(sizeof(struct mmc_command), GFP_KERNEL);
> +       if (!cmd)
> +               goto free_mrq;
> +
> +       stop = kzalloc(sizeof(struct mmc_command), GFP_KERNEL);
> +       if (!stop)
> +               goto free_cmd;
> +
> +       data = kzalloc(sizeof(struct mmc_data), GFP_KERNEL);
> +       if (!data)
> +               goto free_stop;
> +
> +       mrq->cmd = cmd;
> +       mrq->data = data;
> +       mrq->stop = stop;
> +       cxt->mrq = mrq;
> +
> +       info->major = MMC_BLOCK_MAJOR;
> +       info->flags = PSTORE_FLAGS_DMESG;
> +       info->panic_write = mmcpstore_panic_write;
> +       ret = register_pstore_blk(info);
> +       if (ret) {
> +               pr_err("%s registering with psblk failed (%d)\n",
> +                               cxt->dev_name, ret);
> +               goto free_data;
> +       }
> +
> +       pr_info("%s registered as psblk backend\n", cxt->dev_name);
> +       return;
> +
> +free_data:
> +       kfree(data);
> +free_stop:
> +       kfree(stop);
> +free_cmd:
> +       kfree(cmd);
> +free_mrq:
> +       kfree(mrq);
> +out:
> +       return;
> +}
> +
> +void unregister_mmcpstore(void)
> +{
> +       struct mmcpstore_context *cxt = &oops_cxt;
> +
> +       unregister_pstore_blk(MMC_BLOCK_MAJOR);
> +       kfree(cxt->mrq->data);
> +       kfree(cxt->mrq->stop);
> +       kfree(cxt->mrq->cmd);
> +       kfree(cxt->mrq);
> +       cxt->card = NULL;
> +}
> diff --git a/include/linux/mmc/core.h b/include/linux/mmc/core.h
> index 29aa50711626..53840a361b5a 100644
> --- a/include/linux/mmc/core.h
> +++ b/include/linux/mmc/core.h
> @@ -166,6 +166,11 @@ struct mmc_request {
>
>  struct mmc_card;
>
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +void mmc_wait_for_pstore_req(struct mmc_host *host, struct mmc_request *mrq);
> +int mmc_claim_host_async(struct mmc_host *host);
> +#endif
> +
>  void mmc_wait_for_req(struct mmc_host *host, struct mmc_request *mrq);
>  int mmc_wait_for_cmd(struct mmc_host *host, struct mmc_command *cmd,
>                 int retries);
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 01bba36545c5..ba9001498e03 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -178,6 +178,18 @@ struct mmc_host_ops {
>
>         /* Initialize an SD express card, mandatory for MMC_CAP2_SD_EXP. */
>         int     (*init_sd_express)(struct mmc_host *host, struct mmc_ios *ios);
> +
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +       /*
> +        * The following two APIs are introduced to support mmcpstore
> +        * functionality. Cleanup API to terminate the ongoing and
> +        * pending requests before a panic write post, and polling API
> +        * to ensure that write succeeds before the Kernel dies.
> +        */
> +       void    (*req_cleanup_pending)(struct mmc_host *host);
> +       int     (*req_completion_poll)(struct mmc_host *host,
> +                                      unsigned long timeout);
> +#endif
>  };
>
>  struct mmc_cqe_ops {
> --
> 2.17.1
>

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