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Re: [Qemu-devel] [RFC v2 05/33] migration: better error handling with QE
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [RFC v2 05/33] migration: better error handling with QEMUFile |
Date: |
Tue, 26 Sep 2017 09:53:44 +0100 |
User-agent: |
Mutt/1.8.3 (2017-05-23) |
* Peter Xu (address@hidden) wrote:
> On Thu, Sep 21, 2017 at 06:51:37PM +0100, Dr. David Alan Gilbert wrote:
> > * Peter Xu (address@hidden) wrote:
> > > If the postcopy down due to some reason, we can always see this on dst:
> > >
> > > qemu-system-x86_64: RP: Received invalid message 0x0000 length 0x0000
> > >
> > > However in most cases that's not the real issue. The problem is that
> > > qemu_get_be16() has no way to show whether the returned data is valid or
> > > not, and we are _always_ assuming it is valid. That's possibly not wise.
> > >
> > > The best approach to solve this would be: refactoring QEMUFile interface
> > > to allow the APIs to return error if there is. However it needs quite a
> > > bit of work and testing. For now, let's explicitly check the validity
> > > first before using the data in all places for qemu_get_*().
> > >
> > > This patch tries to fix most of the cases I can see. Only if we are with
> > > this, can we make sure we are processing the valid data, and also can we
> > > make sure we can capture the channel down events correctly.
> > >
> > > Signed-off-by: Peter Xu <address@hidden>
> > > ---
> > > migration/migration.c | 5 +++++
> > > migration/ram.c | 22 ++++++++++++++++++----
> > > migration/savevm.c | 41 +++++++++++++++++++++++++++++++++++++++--
> > > 3 files changed, 62 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/migration/migration.c b/migration/migration.c
> > > index c818412..92bf9b8 100644
> > > --- a/migration/migration.c
> > > +++ b/migration/migration.c
> > > @@ -1543,6 +1543,11 @@ static void *source_return_path_thread(void
> > > *opaque)
> > > header_type = qemu_get_be16(rp);
> > > header_len = qemu_get_be16(rp);
> > >
> > > + if (qemu_file_get_error(rp)) {
> > > + mark_source_rp_bad(ms);
> > > + goto out;
> > > + }
> > > +
> > > if (header_type >= MIG_RP_MSG_MAX ||
> > > header_type == MIG_RP_MSG_INVALID) {
> > > error_report("RP: Received invalid message 0x%04x length
> > > 0x%04x",
> > > diff --git a/migration/ram.c b/migration/ram.c
> > > index affb20c..7e20097 100644
> > > --- a/migration/ram.c
> > > +++ b/migration/ram.c
> > > @@ -2417,7 +2417,7 @@ static int ram_load_postcopy(QEMUFile *f)
> > > void *last_host = NULL;
> > > bool all_zero = false;
> > >
> > > - while (!ret && !(flags & RAM_SAVE_FLAG_EOS)) {
> > > + while (!(flags & RAM_SAVE_FLAG_EOS)) {
> >
> > With this change, I don't see what's checking the result of:
> > ret = postcopy_place_page(...)
> > at the bottom of the loop.
>
> Indeed.
>
> I'll add the check after postcopy_place_page().
>
> >
> > > ram_addr_t addr;
> > > void *host = NULL;
> > > void *page_buffer = NULL;
> > > @@ -2426,6 +2426,16 @@ static int ram_load_postcopy(QEMUFile *f)
> > > uint8_t ch;
> > >
> > > addr = qemu_get_be64(f);
> > > +
> > > + /*
> > > + * If qemu file error, we should stop here, and then "addr"
> > > + * may be invalid
> > > + */
> > > + ret = qemu_file_get_error(f);
> > > + if (ret) {
> > > + break;
> > > + }
> > > +
> > > flags = addr & ~TARGET_PAGE_MASK;
> > > addr &= TARGET_PAGE_MASK;
> > >
> > > @@ -2506,6 +2516,13 @@ static int ram_load_postcopy(QEMUFile *f)
> > > error_report("Unknown combination of migration flags: %#x"
> > > " (postcopy mode)", flags);
> > > ret = -EINVAL;
> > > + break;
> > > + }
> > > +
> > > + /* Detect for any possible file errors */
> > > + if (qemu_file_get_error(f)) {
> > > + ret = qemu_file_get_error(f);
> > > + break;
> > > }
> > >
> > > if (place_needed) {
> > > @@ -2520,9 +2537,6 @@ static int ram_load_postcopy(QEMUFile *f)
> > > place_source, block);
> > > }
> > > }
> > > - if (!ret) {
> > > - ret = qemu_file_get_error(f);
> > > - }
> > > }
> > >
> > > return ret;
> > > diff --git a/migration/savevm.c b/migration/savevm.c
> > > index fdd15fa..7172f14 100644
> > > --- a/migration/savevm.c
> > > +++ b/migration/savevm.c
> > > @@ -1720,6 +1720,11 @@ static int loadvm_process_command(QEMUFile *f)
> > > cmd = qemu_get_be16(f);
> > > len = qemu_get_be16(f);
> > >
> > > + /* Check validity before continue processing of cmds */
> > > + if (qemu_file_get_error(f)) {
> > > + return qemu_file_get_error(f);
> > > + }
> > > +
> > > trace_loadvm_process_command(cmd, len);
> > > if (cmd >= MIG_CMD_MAX || cmd == MIG_CMD_INVALID) {
> > > error_report("MIG_CMD 0x%x unknown (len 0x%x)", cmd, len);
> > > @@ -1785,6 +1790,7 @@ static int loadvm_process_command(QEMUFile *f)
> > > */
> > > static bool check_section_footer(QEMUFile *f, SaveStateEntry *se)
> > > {
> > > + int ret;
> > > uint8_t read_mark;
> > > uint32_t read_section_id;
> > >
> > > @@ -1795,6 +1801,13 @@ static bool check_section_footer(QEMUFile *f,
> > > SaveStateEntry *se)
> > >
> > > read_mark = qemu_get_byte(f);
> > >
> > > + ret = qemu_file_get_error(f);
> > > + if (ret) {
> > > + error_report("%s: Read section footer failed: %d",
> > > + __func__, ret);
> > > + return false;
> > > + }
> > > +
> > > if (read_mark != QEMU_VM_SECTION_FOOTER) {
> > > error_report("Missing section footer for %s", se->idstr);
> > > return false;
> > > @@ -1830,6 +1843,13 @@ qemu_loadvm_section_start_full(QEMUFile *f,
> > > MigrationIncomingState *mis)
> > > instance_id = qemu_get_be32(f);
> > > version_id = qemu_get_be32(f);
> > >
> > > + ret = qemu_file_get_error(f);
> > > + if (ret) {
> > > + error_report("%s: Failed to read instance/version ID: %d",
> > > + __func__, ret);
> > > + return ret;
> > > + }
> > > +
> > > trace_qemu_loadvm_state_section_startfull(section_id, idstr,
> > > instance_id, version_id);
> > > /* Find savevm section */
> > > @@ -1877,6 +1897,13 @@ qemu_loadvm_section_part_end(QEMUFile *f,
> > > MigrationIncomingState *mis)
> > >
> > > section_id = qemu_get_be32(f);
> > >
> > > + ret = qemu_file_get_error(f);
> > > + if (ret) {
> > > + error_report("%s: Failed to read section ID: %d",
> > > + __func__, ret);
> > > + return ret;
> > > + }
> > > +
> > > trace_qemu_loadvm_state_section_partend(section_id);
> > > QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
> > > if (se->load_section_id == section_id) {
> > > @@ -1944,8 +1971,14 @@ static int qemu_loadvm_state_main(QEMUFile *f,
> > > MigrationIncomingState *mis)
> > > uint8_t section_type;
> > > int ret = 0;
> > >
> > > - while ((section_type = qemu_get_byte(f)) != QEMU_VM_EOF) {
> > > - ret = 0;
> > > + while (true) {
> > > + section_type = qemu_get_byte(f);
> > > +
> > > + if (qemu_file_get_error(f)) {
> > > + ret = qemu_file_get_error(f);
> > > + break;
> > > + }
> > > +
> > > trace_qemu_loadvm_state_section(section_type);
> > > switch (section_type) {
> > > case QEMU_VM_SECTION_START:
> > > @@ -1969,6 +2002,10 @@ static int qemu_loadvm_state_main(QEMUFile *f,
> > > MigrationIncomingState *mis)
> > > goto out;
> > > }
> > > break;
> > > + case QEMU_VM_EOF:
> > > + /* This is the end of migration */
> > > + goto out;
> > > + break;
> >
> > You don't need the goto and the break (although it does no harm).
>
> I still need the goto to break the loop? (I think a single break will
> only break the select, but not the loop)
>
> If I remove both "goto" and "break", it'll fall through to default, I
> suppose that's not what we want?
No, but if you have the 'goto' you don't need the 'break'.
Dave
> >
> > Dave
> >
> > > default:
> > > error_report("Unknown savevm section type %d", section_type);
> > > ret = -EINVAL;
> > > --
> > > 2.7.4
> > >
> > >
> > --
> > Dr. David Alan Gilbert / address@hidden / Manchester, UK
>
> --
> Peter Xu
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK