| Message ID | 20170405074700.29871-2-vbabka@suse.cz (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On Wed 05-04-17 09:46:57, Vlastimil Babka wrote: > The function __alloc_pages_direct_compact() sets PF_MEMALLOC to prevent > deadlock during page migration by lock_page() (see the comment in > __unmap_and_move()). Then it unconditionally clears the flag, which can clear a > pre-existing PF_MEMALLOC flag and result in recursive reclaim. This was not a > problem until commit a8161d1ed609 ("mm, page_alloc: restructure direct > compaction handling in slowpath"), because direct compation was called only > after direct reclaim, which was skipped when PF_MEMALLOC flag was set. > > Even now it's only a theoretical issue, as the new callsite of > __alloc_pages_direct_compact() is reached only for costly orders and when > gfp_pfmemalloc_allowed() is true, which means either __GFP_NOMEMALLOC is in > gfp_flags or in_interrupt() is true. There is no such known context, but let's > play it safe and make __alloc_pages_direct_compact() robust for cases where > PF_MEMALLOC is already set. > > Fixes: a8161d1ed609 ("mm, page_alloc: restructure direct compaction handling in slowpath") > Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > Signed-off-by: Vlastimil Babka <vbabka@suse.cz> > Cc: <stable@vger.kernel.org> Acked-by: Michal Hocko <mhocko@suse.com> > --- > mm/page_alloc.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3589f8be53be..b84e6ffbe756 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3288,6 +3288,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, > enum compact_priority prio, enum compact_result *compact_result) > { > struct page *page; > + unsigned int noreclaim_flag = current->flags & PF_MEMALLOC; > > if (!order) > return NULL; > @@ -3295,7 +3296,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, > current->flags |= PF_MEMALLOC; > *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac, > prio); > - current->flags &= ~PF_MEMALLOC; > + current->flags = (current->flags & ~PF_MEMALLOC) | noreclaim_flag; > > if (*compact_result <= COMPACT_INACTIVE) > return NULL; > -- > 2.12.2
On 04/05/2017 10:46 AM, Vlastimil Babka wrote: > The function __alloc_pages_direct_compact() sets PF_MEMALLOC to prevent > deadlock during page migration by lock_page() (see the comment in > __unmap_and_move()). Then it unconditionally clears the flag, which can clear a > pre-existing PF_MEMALLOC flag and result in recursive reclaim. This was not a > problem until commit a8161d1ed609 ("mm, page_alloc: restructure direct > compaction handling in slowpath"), because direct compation was called only > after direct reclaim, which was skipped when PF_MEMALLOC flag was set. > > Even now it's only a theoretical issue, as the new callsite of > __alloc_pages_direct_compact() is reached only for costly orders and when > gfp_pfmemalloc_allowed() is true, which means either __GFP_NOMEMALLOC is in is false > gfp_flags or in_interrupt() is true. There is no such known context, but let's > play it safe and make __alloc_pages_direct_compact() robust for cases where > PF_MEMALLOC is already set. > > Fixes: a8161d1ed609 ("mm, page_alloc: restructure direct compaction handling in slowpath") > Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > Signed-off-by: Vlastimil Babka <vbabka@suse.cz> > Cc: <stable@vger.kernel.org> > --- > mm/page_alloc.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3589f8be53be..b84e6ffbe756 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3288,6 +3288,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, > enum compact_priority prio, enum compact_result *compact_result) > { > struct page *page; > + unsigned int noreclaim_flag = current->flags & PF_MEMALLOC; > > if (!order) > return NULL; > @@ -3295,7 +3296,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, > current->flags |= PF_MEMALLOC; > *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac, > prio); > - current->flags &= ~PF_MEMALLOC; > + current->flags = (current->flags & ~PF_MEMALLOC) | noreclaim_flag; Perhaps this would look better: tsk_restore_flags(current, noreclaim_flag, PF_MEMALLOC); ? > if (*compact_result <= COMPACT_INACTIVE) > return NULL; >
On April 05, 2017 3:47 PM Vlastimil Babka wrote: > > The function __alloc_pages_direct_compact() sets PF_MEMALLOC to prevent > deadlock during page migration by lock_page() (see the comment in > __unmap_and_move()). Then it unconditionally clears the flag, which can clear a > pre-existing PF_MEMALLOC flag and result in recursive reclaim. This was not a > problem until commit a8161d1ed609 ("mm, page_alloc: restructure direct > compaction handling in slowpath"), because direct compation was called only > after direct reclaim, which was skipped when PF_MEMALLOC flag was set. > > Even now it's only a theoretical issue, as the new callsite of > __alloc_pages_direct_compact() is reached only for costly orders and when > gfp_pfmemalloc_allowed() is true, which means either __GFP_NOMEMALLOC is in > gfp_flags or in_interrupt() is true. There is no such known context, but let's > play it safe and make __alloc_pages_direct_compact() robust for cases where > PF_MEMALLOC is already set. > > Fixes: a8161d1ed609 ("mm, page_alloc: restructure direct compaction handling in slowpath") > Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > Signed-off-by: Vlastimil Babka <vbabka@suse.cz> > Cc: <stable@vger.kernel.org> > --- Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com> > mm/page_alloc.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3589f8be53be..b84e6ffbe756 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3288,6 +3288,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, > enum compact_priority prio, enum compact_result *compact_result) > { > struct page *page; > + unsigned int noreclaim_flag = current->flags & PF_MEMALLOC; > > if (!order) > return NULL; > @@ -3295,7 +3296,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, > current->flags |= PF_MEMALLOC; > *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac, > prio); > - current->flags &= ~PF_MEMALLOC; > + current->flags = (current->flags & ~PF_MEMALLOC) | noreclaim_flag; > > if (*compact_result <= COMPACT_INACTIVE) > return NULL; > -- > 2.12.2
On 04/05/2017 01:40 PM, Andrey Ryabinin wrote: > On 04/05/2017 10:46 AM, Vlastimil Babka wrote: >> The function __alloc_pages_direct_compact() sets PF_MEMALLOC to prevent >> deadlock during page migration by lock_page() (see the comment in >> __unmap_and_move()). Then it unconditionally clears the flag, which can clear a >> pre-existing PF_MEMALLOC flag and result in recursive reclaim. This was not a >> problem until commit a8161d1ed609 ("mm, page_alloc: restructure direct >> compaction handling in slowpath"), because direct compation was called only >> after direct reclaim, which was skipped when PF_MEMALLOC flag was set. >> >> Even now it's only a theoretical issue, as the new callsite of >> __alloc_pages_direct_compact() is reached only for costly orders and when >> gfp_pfmemalloc_allowed() is true, which means either __GFP_NOMEMALLOC is in > is false > >> gfp_flags or in_interrupt() is true. There is no such known context, but let's >> play it safe and make __alloc_pages_direct_compact() robust for cases where >> PF_MEMALLOC is already set. >> >> Fixes: a8161d1ed609 ("mm, page_alloc: restructure direct compaction handling in slowpath") >> Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com> >> Signed-off-by: Vlastimil Babka <vbabka@suse.cz> >> Cc: <stable@vger.kernel.org> >> --- >> mm/page_alloc.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 3589f8be53be..b84e6ffbe756 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -3288,6 +3288,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, >> enum compact_priority prio, enum compact_result *compact_result) >> { >> struct page *page; >> + unsigned int noreclaim_flag = current->flags & PF_MEMALLOC; >> >> if (!order) >> return NULL; >> @@ -3295,7 +3296,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, >> current->flags |= PF_MEMALLOC; >> *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac, >> prio); >> - current->flags &= ~PF_MEMALLOC; >> + current->flags = (current->flags & ~PF_MEMALLOC) | noreclaim_flag; > > Perhaps this would look better: > > tsk_restore_flags(current, noreclaim_flag, PF_MEMALLOC); > > ? Well, I didn't care much considering this is for stable only, and patch 2/4 rewrites this to the new api. >> if (*compact_result <= COMPACT_INACTIVE) >> return NULL; >> >
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3589f8be53be..b84e6ffbe756 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3288,6 +3288,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, enum compact_priority prio, enum compact_result *compact_result) { struct page *page; + unsigned int noreclaim_flag = current->flags & PF_MEMALLOC; if (!order) return NULL; @@ -3295,7 +3296,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, current->flags |= PF_MEMALLOC; *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac, prio); - current->flags &= ~PF_MEMALLOC; + current->flags = (current->flags & ~PF_MEMALLOC) | noreclaim_flag; if (*compact_result <= COMPACT_INACTIVE) return NULL;
The function __alloc_pages_direct_compact() sets PF_MEMALLOC to prevent deadlock during page migration by lock_page() (see the comment in __unmap_and_move()). Then it unconditionally clears the flag, which can clear a pre-existing PF_MEMALLOC flag and result in recursive reclaim. This was not a problem until commit a8161d1ed609 ("mm, page_alloc: restructure direct compaction handling in slowpath"), because direct compation was called only after direct reclaim, which was skipped when PF_MEMALLOC flag was set. Even now it's only a theoretical issue, as the new callsite of __alloc_pages_direct_compact() is reached only for costly orders and when gfp_pfmemalloc_allowed() is true, which means either __GFP_NOMEMALLOC is in gfp_flags or in_interrupt() is true. There is no such known context, but let's play it safe and make __alloc_pages_direct_compact() robust for cases where PF_MEMALLOC is already set. Fixes: a8161d1ed609 ("mm, page_alloc: restructure direct compaction handling in slowpath") Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Cc: <stable@vger.kernel.org> --- mm/page_alloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)