Re: [PATCH 2/3] remoteproc: Add inline coredump functionality

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Fri 17 Apr 00:52 PDT 2020, Loic PALLARDY wrote:

> Hi Rishabh,
> 
> > -----Original Message-----
> > From: linux-remoteproc-owner@vger.kernel.org <linux-remoteproc-
> > owner@vger.kernel.org> On Behalf Of Rishabh Bhatnagar
> > Sent: jeudi 16 avril 2020 20:39
> > To: linux-remoteproc@vger.kernel.org; linux-kernel@vger.kernel.org
> > Cc: bjorn.andersson@linaro.org; ohad@wizery.com;
> > mathieu.poirier@linaro.org; tsoni@codeaurora.org;
> > psodagud@codeaurora.org; sidgup@codeaurora.org; Rishabh Bhatnagar
> > <rishabhb@codeaurora.org>
> > Subject: [PATCH 2/3] remoteproc: Add inline coredump functionality
> > 
> > This patch adds the inline coredump functionality. 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_coredump.c | 130
> > +++++++++++++++++++++++++++++++
> >  drivers/remoteproc/remoteproc_internal.h |  23 +++++-
> >  include/linux/remoteproc.h               |   2 +
> >  3 files changed, 153 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/remoteproc/remoteproc_coredump.c
> > b/drivers/remoteproc/remoteproc_coredump.c
> > index 9de0467..888b7dec91 100644
> > --- a/drivers/remoteproc/remoteproc_coredump.c
> > +++ b/drivers/remoteproc/remoteproc_coredump.c
> > @@ -12,6 +12,84 @@
> >  #include <linux/remoteproc.h>
> >  #include "remoteproc_internal.h"
> > 
> > +static void rproc_free_dump(void *data)
> > +{
> > +	struct rproc_coredump_state *dump_state = data;
> > +
> > +	complete(&dump_state->dump_done);
> > +}
> > +
> > +static unsigned long resolve_addr(loff_t user_offset,
> > +				   struct list_head *segments,
> > +				   unsigned long *data_left)
> > +{
> > +	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 header_size)
> > +{
> > +	void *device_mem;
> > +	size_t data_left, copy_size, bytes_left = count;
> > +	unsigned long addr;
> > +	struct rproc_coredump_state *dump_state = data;
> > +	struct rproc *rproc = dump_state->rproc;
> > +	void *elfcore = dump_state->header;
> > +
> > +	/* Copy the header first */
> > +	if (offset < header_size) {
> > +		copy_size = header_size - offset;
> > +		copy_size = min(copy_size, bytes_left);
> > +
> > +		memcpy(buffer, elfcore + offset, copy_size);
> > +		offset += copy_size;
> > +		bytes_left -= copy_size;
> > +		buffer += copy_size;
> > +	}
> > +
> > +	while (bytes_left) {
> > +		addr = resolve_addr(offset - header_size,
> > +				    &rproc->dump_segments, &data_left);
> > +		/* EOF check */
> > +		if (data_left == 0) {
> > +			pr_info("Ramdump complete %lld bytes read",
> > offset);
> > +			break;
> > +		}
> > +
> > +		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("Address:%lx with size %zd out of remoteproc
> > carveout\n",
> > +				addr, copy_size);
> > +			return -ENOMEM;
> > +		}
> > +		memcpy(buffer, device_mem, copy_size);
> > +
> > +		offset += copy_size;
> > +		buffer += copy_size;
> > +		bytes_left -= copy_size;
> > +	}
> > +
> > +	return count - bytes_left;
> > +}
> > +
> >  static void create_elf_header(void *data, int phnum, struct rproc *rproc)
> >  {
> >  	struct elf32_phdr *phdr;
> > @@ -55,6 +133,58 @@ static void create_elf_header(void *data, int phnum,
> > struct rproc *rproc)
> >  }
> > 
> >  /**
> > + * rproc_inline_coredump() - perform synchronized coredump
> > + * @rproc:	rproc handle
> > + *
> > + * This function will generate an ELF header for the registered segments
> > + * and create a devcoredump device associated with rproc. This function
> > + * directly copies the segments from device memory to userspace. The
> > + * recovery is stalled until the enitire coredump is read. This approach
> Typo entire -> entire
> > + * avoids using extra vmalloc memory(which can be really large).
> > + */
> > +void rproc_inline_coredump(struct rproc *rproc)
> > +{
> > +	struct rproc_dump_segment *segment;
> > +	struct elf32_phdr *phdr;
> > +	struct elf32_hdr *ehdr;
> > +	struct rproc_coredump_state *dump_state;
> > +	size_t header_size;
> > +	void *data;
> > +	int phnum = 0;
> > +
> > +	if (list_empty(&rproc->dump_segments))
> > +		return;
> > +
> > +	header_size = sizeof(*ehdr);
> > +	list_for_each_entry(segment, &rproc->dump_segments, node) {
> > +		header_size += sizeof(*phdr);
> > +
> > +		phnum++;
> > +	}
> > +
> > +	data = vmalloc(header_size);
> > +	if (!data)
> > +		return;
> > +
> > +	ehdr = data;
> > +	create_elf_header(data, phnum, rproc);
> > +
> > +	dump_state = kzalloc(sizeof(*dump_state), GFP_KERNEL);
> > +	dump_state->rproc = rproc;
> > +	dump_state->header = data;
> > +	init_completion(&dump_state->dump_done);
> > +
> > +	dev_coredumpm(&rproc->dev, NULL, dump_state, header_size,
> > GFP_KERNEL,
> > +		      rproc_read_dump, rproc_free_dump);
> > +
> > +	/* Wait until the dump is read and free is called */
> > +	wait_for_completion(&dump_state->dump_done);
> 
> Maybe good to add a timeout with value programmable via debugfs?
> 

devcoredump provides a timeout already, although not configurable today.
I believe this is sufficient, but a mentioning in the comment would be
useful.

Regards,
Bjorn