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
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.
~Andrew
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