On Tue, Jul 6, 2021 at 10:41 AM 王擎 <wangqing@xxxxxxxx> wrote: > > > >On Mon, Jul 5, 2021 at 9:57 PM Wang Qing <wangqing@xxxxxxxx> wrote: > >> > >> Use GFP_ATOMIC when local_lock_irqsave in __alloc_pages_bulk > >> > >> Reported-by: syzbot+e45919db2eab5e837646@xxxxxxxxxxxxxxxxxxxxxxxxx > >> Signed-off-by: Wang Qing <wangqing@xxxxxxxx> > >> --- > >> mm/page_alloc.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > >> index d6e94cc..3016ba5 > >> --- a/mm/page_alloc.c > >> +++ b/mm/page_alloc.c > >> @@ -5309,7 +5309,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, > >> } > >> nr_account++; > >> > >> - prep_new_page(page, 0, gfp, 0); > >> + prep_new_page(page, 0, gfp | GFP_ATOMIC, 0); > > > >Hi Wang Qing, > > > >I didn't get the point here. IIUC, prep_new_page() will not allocate > >memory. So why do we need GFP_ATOMIC? What I missed here? > > > >Thanks. > > prep_new_page() will allocate memory in some scenarios. For details, > you can check the bugs detected by syzkaller: > https://syzkaller.appspot.com/bug?id=91c2030241ada0e5d21877f8f2f44c98cffc04bb > > Call Trace: > __dump_stack lib/dump_stack.c:79 [inline] > dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:96 > ___might_sleep.cold+0x1f1/0x237 kernel/sched/core.c:9153 > prepare_alloc_pages+0x3da/0x580 mm/page_alloc.c:5179 > __alloc_pages+0x12f/0x500 mm/page_alloc.c:5375 > alloc_pages+0x18c/0x2a0 mm/mempolicy.c:2272 > stack_depot_save+0x39d/0x4e0 lib/stackdepot.c:303 > save_stack+0x15e/0x1e0 mm/page_owner.c:120 > __set_page_owner+0x50/0x290 mm/page_owner.c:181 > prep_new_page mm/page_alloc.c:2445 [inline] > __alloc_pages_bulk+0x8b9/0x1870 mm/page_alloc.c:5313 Got it. But I don't think the fix you mentioned above was appropriate. What if GFP_KERNEL | GFP_ATOMIC? Thanks. > > Thanks. > > Qing > > > > >> if (page_list) > >> list_add(&page->lru, page_list); > >> else > >> -- > >> 2.7.4 > >> > >
