Re: [PATCH] colo: fix return without releasing RCU

[Zhang, Chen]

On 12/13/2019 11:03 PM, Dr. David Alan Gilbert wrote:
> * Paolo Bonzini (address@hidden) wrote:
> > Use WITH_RCU_READ_LOCK_GUARD to avoid exiting colo_init_ram_cache
> > without releasing RCU.
> >
> > Cc: Dr. David Alan Gilbert <address@hidden>
> > Signed-off-by: Paolo Bonzini <address@hidden>
> Reviewed-by: Dr. David Alan Gilbert <address@hidden>

Reviewed-by: Zhang Chen <address@hidden>


> > ---
> >   migration/ram.c | 33 +++++++++++++++++----------------
> >   1 file changed, 17 insertions(+), 16 deletions(-)
> >
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 7dd7f81..8d7c015 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -3891,26 +3891,27 @@ int colo_init_ram_cache(void)
> >   {
> >       RAMBlock *block;
> >   
> > -    rcu_read_lock();
> > -    RAMBLOCK_FOREACH_NOT_IGNORED(block) {
> > -        block->colo_cache = qemu_anon_ram_alloc(block->used_length,
> > -                                                NULL,
> > -                                                false);
> > -        if (!block->colo_cache) {
> > -            error_report("%s: Can't alloc memory for COLO cache of block %s,"
> > -                         "size 0x" RAM_ADDR_FMT, __func__, block->idstr,
> > -                         block->used_length);
> > -            RAMBLOCK_FOREACH_NOT_IGNORED(block) {
> > -                if (block->colo_cache) {
> > -                    qemu_anon_ram_free(block->colo_cache, block->used_length);
> > -                    block->colo_cache = NULL;
> > +    WITH_RCU_READ_LOCK_GUARD() {
> > +        RAMBLOCK_FOREACH_NOT_IGNORED(block) {
> > +            block->colo_cache = qemu_anon_ram_alloc(block->used_length,
> > +                                                    NULL,
> > +                                                    false);
> > +            if (!block->colo_cache) {
> > +                error_report("%s: Can't alloc memory for COLO cache of block 
> > %s,"
> > +                             "size 0x" RAM_ADDR_FMT, __func__, block->idstr,
> > +                             block->used_length);
> > +                RAMBLOCK_FOREACH_NOT_IGNORED(block) {
> > +                    if (block->colo_cache) {
> > +                        qemu_anon_ram_free(block->colo_cache, 
> > block->used_length);
> > +                        block->colo_cache = NULL;
> > +                    }
> >                   }
> > +                return -errno;
> >               }
> > -            return -errno;
> > +            memcpy(block->colo_cache, block->host, block->used_length);
> >           }
> > -        memcpy(block->colo_cache, block->host, block->used_length);
> >       }
> > -    rcu_read_unlock();
> > +
> >       /*
> >       * Record the dirty pages that sent by PVM, we use this dirty bitmap 
> > together
> >       * with to decide which page in cache should be flushed into SVM's RAM. 
> > Here
> > --
> > 1.8.3.1
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK