On 4/29/19 3:49 PM, Andrew Cooper wrote:
> On 29/04/2019 15:46, George Dunlap wrote:
>> On 4/29/19 3:32 PM, George Dunlap wrote:
>>> On 4/26/19 6:21 PM, Tamas K Lengyel wrote:
>>>> Calling _put_page_type while also holding the page_lock
>>>> for that page can cause a deadlock.
>>>>
>>>> Signed-off-by: Tamas K Lengyel <ta...@tklengyel.com>
>>>> Cc: Jan Beulich <jbeul...@suse.com>
>>>> Cc: Andrew Cooper <andrew.coop...@citrix.com>
>>>> Cc: George Dunlap <george.dun...@eu.citrix.com>
>>>> Cc: Wei Liu <wei.l...@citrix.com>
>>>> Cc: Roger Pau Monne <roger....@citrix.com>
>>>> ---
>>>> v3: simplified patch by keeping the additional references already in-place
>>>> ---
>>>> xen/arch/x86/mm/mem_sharing.c | 19 ++++++++++---------
>>>> 1 file changed, 10 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
>>>> index dfc279d371..e2f74ac770 100644
>>>> --- a/xen/arch/x86/mm/mem_sharing.c
>>>> +++ b/xen/arch/x86/mm/mem_sharing.c
>>>> @@ -648,10 +648,6 @@ static int page_make_private(struct domain *d, struct
>>>> page_info *page)
>>>> return -EBUSY;
>>>> }
>>>>
>>>> - /* We can only change the type if count is one */
>>>> - /* Because we are locking pages individually, we need to drop
>>>> - * the lock here, while the page is typed. We cannot risk the
>>>> - * race of page_unlock and then put_page_type. */
>>>> expected_type = (PGT_shared_page | PGT_validated | PGT_locked | 2);
>>>> if ( page->u.inuse.type_info != expected_type )
>>>> {
>>>> @@ -660,12 +656,12 @@ static int page_make_private(struct domain *d,
>>>> struct page_info *page)
>>>> return -EEXIST;
>>>> }
>>>>
>>>> - /* Drop the final typecount */
>>>> - put_page_and_type(page);
>>>> -
>>>> /* Now that we've dropped the type, we can unlock */
>>>> mem_sharing_page_unlock(page);
>>>>
>>>> + /* Drop the final typecount */
>>>> + put_page_and_type(page);
>>>> +
>>>> /* Change the owner */
>>>> ASSERT(page_get_owner(page) == dom_cow);
>>>> page_set_owner(page, d);
>>>> @@ -900,6 +896,7 @@ static int share_pages(struct domain *sd, gfn_t sgfn,
>>>> shr_handle_t sh,
>>>> p2m_type_t smfn_type, cmfn_type;
>>>> struct two_gfns tg;
>>>> struct rmap_iterator ri;
>>>> + unsigned long put_count = 0;
>>>>
>>>> get_two_gfns(sd, sgfn, &smfn_type, NULL, &smfn,
>>>> cd, cgfn, &cmfn_type, NULL, &cmfn, 0, &tg);
>>>> @@ -984,7 +981,7 @@ static int share_pages(struct domain *sd, gfn_t sgfn,
>>>> shr_handle_t sh,
>>>> * Don't change the type of rmap for the client page. */
>>>> rmap_del(gfn, cpage, 0);
>>>> rmap_add(gfn, spage);
>>>> - put_page_and_type(cpage);
>>>> + put_count++;
>>>> d = get_domain_by_id(gfn->domain);
>>>> BUG_ON(!d);
>>>> BUG_ON(set_shared_p2m_entry(d, gfn->gfn, smfn));
>>>> @@ -999,6 +996,10 @@ static int share_pages(struct domain *sd, gfn_t sgfn,
>>>> shr_handle_t sh,
>>>> mem_sharing_page_unlock(secondpg);
>>>> mem_sharing_page_unlock(firstpg);
>>>>
>>>> + BUG_ON(!put_count);
>>>> + while ( put_count-- )
>>>> + put_page_and_type(cpage);
>>>> +
>>>> /* Free the client page */
>>>> if(test_and_clear_bit(_PGC_allocated, &cpage->count_info))
>>>> put_page(cpage);
>>>> @@ -1167,8 +1168,8 @@ int __mem_sharing_unshare_page(struct domain *d,
>>>> {
>>>> if ( !last_gfn )
>>>> mem_sharing_gfn_destroy(page, d, gfn_info);
>>>> - put_page_and_type(page);
>>>> mem_sharing_page_unlock(page);
>>>> + put_page_and_type(page);
>>>> if ( last_gfn )
>>>> {
>>>> if ( !get_page(page, dom_cow) )
>>> ...Probably should have mentioned that this needs to be applied after
>>> your other patch. :-)
>> Hmm -- actually, the base appears to be a non-publicly-available tree
>> (Andy's private x86-next).
>
> Its perfectly public
>
> http://xenbits.xen.org/gitweb/?p=people/andrewcoop/xen.git;a=shortlog;h=refs/heads/x86-next
OK, didn't realize this.
>
> and has been in effect during commit freezes for the past several years
> worth of releases.
>
> It is fine to post a tree based on something other than xen.git/staging
> so long as the cover letter identifies where the series is based. A lot
> of development already occurs in this way on xen-devel.
I agree it's fine when a URL is provided.
-George
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