On Fri, Mar 24, 2017 at 11:51:53AM +0100, Peter Zijlstra wrote:
> On Fri, Mar 24, 2017 at 01:24:36PM +0300, Kirill A. Shutemov wrote:
>
> > I'm not sure what is the best way to fix this.
> > Few options:
> > - Drop the VM_BUG();
> > - Bump preempt count during __get_user_pages_fast();
> > - Use get_page() instead of page_cache_get_speculative() on x86.
> >
> > Any opinions?
>
> I think I'm in favour of the first; either remove or amend to include
> irqs_disabled() or so.
>
> This in favour of keeping the variants of GUP down.
Something like this?
-------------------8<-----------------------
>From d2f416a3ee3e5dbb10e59d0b374d382fdc4ba082 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Date: Fri, 24 Mar 2017 14:13:05 +0300
Subject: [PATCH] mm: Fix false-positive VM_BUG_ON() in
page_cache_{get,add}_speculative
0day triggered this:
kernel BUG at include/linux/pagemap.h:151!
invalid opcode: 0000 [#1]
CPU: 0 PID: 458 Comm: trinity-c0 Not tainted 4.11.0-rc2-00251-g2947ba0 #1
task: ffff88001f19ab00 task.stack: ffff88001f084000
RIP: 0010:gup_pud_range+0x56f/0x63d
RSP: 0018:ffff88001f087ba8 EFLAGS: 00010046
RAX: 0000000080000000 RBX: 000000000164e000 RCX: ffff88001e0badc0
RDX: dead000000000100 RSI: 0000000000000001 RDI: ffff88001e0badc0
RBP: ffff88001f087c38 R08: ffff88001f087cf8 R09: ffff88001f087c6c
R10: 0000000000000000 R11: ffff88001f19b0f0 R12: ffff88001f087c6c
R13: ffff88001e0badc0 R14: 800000001e7b7867 R15: 0000000000000000
FS: 00007f7ea7b60700(0000) GS:ffffffffae02f000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000013eb130 CR3: 0000000017ddb000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 00000000000d0602
Call Trace:
__get_user_pages_fast+0x107/0x136
get_user_pages_fast+0x78/0x89
get_futex_key+0xfd/0x350
? simple_write_end+0x83/0xbe
futex_requeue+0x1a3/0x585
do_futex+0x834/0x86f
? kvm_clock_read+0x16/0x1e
? paravirt_sched_clock+0x9/0xd
? lock_release+0x11e/0x328
SyS_futex+0x125/0x135
? write_seqcount_end+0x1a/0x1f
? vtime_account_user+0x4b/0x50
do_syscall_64+0x61/0x74
entry_SYSCALL64_slow_path+0x25/0x25
It' VM_BUG_ON() due to false-negative in_atomic(). We call
page_cache_get_speculative() with disabled local interrupts.
It should be atomic enough.
Let's check for disabled interrupts in the VM_BUG_ON() too.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reported-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
---
include/linux/pagemap.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index f84cf5f76366..e7bbd9d4dc6c 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -148,7 +148,7 @@ static inline int page_cache_get_speculative(struct page *page)
#ifdef CONFIG_TINY_RCU
# ifdef CONFIG_PREEMPT_COUNT
- VM_BUG_ON(!in_atomic());
+ VM_BUG_ON(!in_atomic() && !irqs_disabled());
# endif
/*
* Preempt must be disabled here - we rely on rcu_read_lock doing
@@ -186,7 +186,7 @@ static inline int page_cache_add_speculative(struct page *page, int count)
#if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
# ifdef CONFIG_PREEMPT_COUNT
- VM_BUG_ON(!in_atomic());
+ VM_BUG_ON(!in_atomic() && !irqs_disabled());
# endif
VM_BUG_ON_PAGE(page_count(page) == 0, page);
page_ref_add(page, count);
--
Kirill A. Shutemov
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