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Date:   Wed, 1 Apr 2020 12:51:14 -0700
From:   Bjorn Andersson <bjorn.andersson@linaro.org>
To:     Rishabh Bhatnagar <rishabhb@codeaurora.org>
Cc:     linux-kernel@vger.kernel.org, linux-remoteproc@vger.kernel.org,
        ohad@wizery.com, psodagud@codeaurora.org, tsoni@codeaurora.org,
        sidgup@codeaurora.org
Subject: Re: [PATCH] remoteproc: core: Add a memory efficient coredump
 function
Message-ID: <20200401195114.GD267644@minitux>
References: <1585353412-19644-1-git-send-email-rishabhb@codeaurora.org>
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On Fri 27 Mar 16:56 PDT 2020, Rishabh Bhatnagar wrote:

> The current coredump implementation uses vmalloc area to copy
> all the segments. But this might put a lot of strain on low memory
> targets as the firmware size sometimes is in ten's of MBs.
> The situation becomes worse if there are multiple remote processors
> undergoing recovery at the same time.
> This patch directly copies the device memory to userspace buffer
> and avoids extra memory usage. This requires recovery to be halted
> until data is read by userspace and free function is called.
> 
> Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
> ---
>  drivers/remoteproc/remoteproc_core.c | 107 +++++++++++++++++++++++++++++------
>  include/linux/remoteproc.h           |   4 ++
>  2 files changed, 94 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
> index 097f33e..2d881e5 100644
> --- a/drivers/remoteproc/remoteproc_core.c
> +++ b/drivers/remoteproc/remoteproc_core.c
> @@ -1516,6 +1516,86 @@ int rproc_coredump_add_segment(struct rproc *rproc, dma_addr_t da, size_t size)
>  }
>  EXPORT_SYMBOL(rproc_coredump_add_segment);
>  
> +
> +void rproc_free_dump(void *data)

static

> +{
> +	struct rproc *rproc = data;
> +
> +	dev_info(&rproc->dev, "Userspace done reading rproc dump\n");

Please drop the info prints throughout.

> +	complete(&rproc->dump_done);
> +}
> +
> +static unsigned long get_offset(loff_t user_offset, struct list_head *segments,
> +				unsigned long *data_left)

Please rename this rproc_coredump_resolve_segment(), or something along
those lines.

> +{
> +	struct rproc_dump_segment *segment;
> +
> +	list_for_each_entry(segment, segments, node) {
> +		if (user_offset >= segment->size)
> +			user_offset -= segment->size;
> +		else
> +			break;
> +	}
> +
> +	if (&segment->node == segments) {
> +		*data_left = 0;
> +		return 0;
> +	}
> +
> +	*data_left = segment->size - user_offset;
> +
> +	return segment->da + user_offset;
> +}
> +
> +static ssize_t rproc_read_dump(char *buffer, loff_t offset, size_t count,
> +				void *data, size_t elfcorelen)
> +{
> +	void *device_mem = NULL;
> +	unsigned long data_left = 0;
> +	unsigned long bytes_left = count;
> +	unsigned long addr = 0;
> +	size_t copy_size = 0;
> +	struct rproc *rproc = data;
> +
> +	if (offset < elfcorelen) {
> +		copy_size = elfcorelen - offset;
> +		copy_size = min(copy_size, bytes_left);
> +
> +		memcpy(buffer, rproc->elfcore + offset, copy_size);
> +		offset += copy_size;
> +		bytes_left -= copy_size;
> +		buffer += copy_size;
> +	}
> +
> +	while (bytes_left) {
> +		addr = get_offset(offset - elfcorelen, &rproc->dump_segments,
> +				&data_left);
> +	/* EOF check */

Indentation, and "if no data left" does indicate that this is the end of
the loop already.

> +		if (data_left == 0) {
> +			pr_info("Ramdump complete. %lld bytes read.", offset);
> +			return 0;

You might have copied data to the buffer, so returning 0 here doesn't
seem right. Presumably instead you should break and return offset -
original offset or something like that.

> +		}
> +
> +		copy_size = min_t(size_t, bytes_left, data_left);
> +
> +		device_mem = rproc->ops->da_to_va(rproc, addr, copy_size);
> +		if (!device_mem) {
> +			pr_err("Unable to ioremap: addr %lx, size %zd\n",
> +				 addr, copy_size);
> +			return -ENOMEM;
> +		}
> +		memcpy(buffer, device_mem, copy_size);
> +
> +		offset += copy_size;
> +		buffer += copy_size;
> +		bytes_left -= copy_size;
> +		dev_dbg(&rproc->dev, "Copied %d bytes to userspace\n",
> +			copy_size);
> +	}
> +
> +	return count;

This should be the number of bytes actually returned, so if count is
larger than the sum of the segment sizes this will be wrong.

> +}
> +
>  /**
>   * rproc_coredump_add_custom_segment() - add custom coredump segment
>   * @rproc:	handle of a remote processor
> @@ -1566,27 +1646,27 @@ static void rproc_coredump(struct rproc *rproc)
>  	struct rproc_dump_segment *segment;
>  	struct elf32_phdr *phdr;
>  	struct elf32_hdr *ehdr;
> -	size_t data_size;
> +	size_t header_size;
>  	size_t offset;
>  	void *data;
> -	void *ptr;
>  	int phnum = 0;
>  
>  	if (list_empty(&rproc->dump_segments))
>  		return;
>  
> -	data_size = sizeof(*ehdr);
> +	header_size = sizeof(*ehdr);
>  	list_for_each_entry(segment, &rproc->dump_segments, node) {
> -		data_size += sizeof(*phdr) + segment->size;
> +		header_size += sizeof(*phdr);
>  
>  		phnum++;
>  	}
>  
> -	data = vmalloc(data_size);
> +	data = vmalloc(header_size);
>  	if (!data)
>  		return;
>  
>  	ehdr = data;
> +	rproc->elfcore = data;

Rather than using a rproc-global variable I would prefer that you create
a new rproc_coredump_state struct that carries the header pointer and
the information needed by the read & free functions.

>  
>  	memset(ehdr, 0, sizeof(*ehdr));
>  	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
> @@ -1618,23 +1698,14 @@ static void rproc_coredump(struct rproc *rproc)
>  
>  		if (segment->dump) {
>  			segment->dump(rproc, segment, data + offset);
> -		} else {
> -			ptr = rproc_da_to_va(rproc, segment->da, segment->size);
> -			if (!ptr) {
> -				dev_err(&rproc->dev,
> -					"invalid coredump segment (%pad, %zu)\n",
> -					&segment->da, segment->size);
> -				memset(data + offset, 0xff, segment->size);
> -			} else {
> -				memcpy(data + offset, ptr, segment->size);
> -			}
> -		}
>  
>  		offset += phdr->p_filesz;
>  		phdr++;
>  	}
> +	dev_coredumpm(&rproc->dev, NULL, rproc, header_size, GFP_KERNEL,
> +			rproc_read_dump, rproc_free_dump);
>  
> -	dev_coredumpv(&rproc->dev, data, data_size, GFP_KERNEL);
> +	wait_for_completion(&rproc->dump_done);

This will mean that recovery handling will break on installations that
doesn't have your ramdump collector - as it will just sit here forever
(5 minutes) waiting for userspace to do its job.

I think we need to device a new sysfs attribute, through which you can
enable the "inline" coredump mechanism. That way recovery would work for
all systems and in your specific case you could reconfigure it - perhaps
once the ramdump collector starts.

Regards,
Bjorn

>  }
>  
>  /**
> @@ -1665,6 +1736,7 @@ int rproc_trigger_recovery(struct rproc *rproc)
>  
>  	/* generate coredump */
>  	rproc_coredump(rproc);
> +	reinit_completion(&rproc->dump_done);
>  
>  	/* load firmware */
>  	ret = request_firmware(&firmware_p, rproc->firmware, dev);
> @@ -2067,6 +2139,7 @@ struct rproc *rproc_alloc(struct device *dev, const char *name,
>  	INIT_LIST_HEAD(&rproc->rvdevs);
>  	INIT_LIST_HEAD(&rproc->subdevs);
>  	INIT_LIST_HEAD(&rproc->dump_segments);
> +	init_completion(&rproc->dump_done);
>  
>  	INIT_WORK(&rproc->crash_handler, rproc_crash_handler_work);
>  
> diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
> index 16ad666..461b235 100644
> --- a/include/linux/remoteproc.h
> +++ b/include/linux/remoteproc.h
> @@ -481,6 +481,8 @@ struct rproc_dump_segment {
>   * @auto_boot: flag to indicate if remote processor should be auto-started
>   * @dump_segments: list of segments in the firmware
>   * @nb_vdev: number of vdev currently handled by rproc
> + * @dump_done: completion variable when dump is complete
> + * @elfcore: pointer to elf header buffer
>   */
>  struct rproc {
>  	struct list_head node;
> @@ -514,6 +516,8 @@ struct rproc {
>  	bool auto_boot;
>  	struct list_head dump_segments;
>  	int nb_vdev;
> +	struct completion dump_done;
> +	void *elfcore;
>  };
>  
>  /**
> -- 
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> a Linux Foundation Collaborative Project