linux-kernel - Re: [PATCH RESEND] mm/hugetlb: Don't call region_abort if region

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Message-Id: <20170329141711.50c183a7bb1bfa75e24d4426@linux-foundation.org>
Date:   Wed, 29 Mar 2017 14:17:11 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [PATCH RESEND] mm/hugetlb: Don't call region_abort if
 region_chg fails

On Wed, 29 Mar 2017 14:08:02 -0700 Mike Kravetz <mike.kravetz@...cle.com> wrote:

> Resending because of typo in Andrew's e-mail when first sent
> 
> Changes to hugetlbfs reservation maps is a two step process.  The first
> step is a call to region_chg to determine what needs to be changed, and
> prepare that change.  This should be followed by a call to call to
> region_add to commit the change, or region_abort to abort the change.
> 
> The error path in hugetlb_reserve_pages called region_abort after a
> failed call to region_chg.  As a result, the adds_in_progress counter
> in the reservation map is off by 1.  This is caught by a VM_BUG_ON
> in resv_map_release when the reservation map is freed.
> 
> syzkaller fuzzer found this bug, that resulted in the following:

I'll change the above to

: syzkaller fuzzer (when using an injected kmalloc failure) found this bug,
: that resulted in the following:

it's important, because this bug won't be triggered (at all easily, at
least) in real-world workloads.

>  kernel BUG at mm/hugetlb.c:742!
>  Call Trace:
>   hugetlbfs_evict_inode+0x7b/0xa0 fs/hugetlbfs/inode.c:493
>   evict+0x481/0x920 fs/inode.c:553
>   iput_final fs/inode.c:1515 [inline]
>   iput+0x62b/0xa20 fs/inode.c:1542
>   hugetlb_file_setup+0x593/0x9f0 fs/hugetlbfs/inode.c:1306
>   newseg+0x422/0xd30 ipc/shm.c:575
>   ipcget_new ipc/util.c:285 [inline]
>   ipcget+0x21e/0x580 ipc/util.c:639
>   SYSC_shmget ipc/shm.c:673 [inline]
>   SyS_shmget+0x158/0x230 ipc/shm.c:657
>   entry_SYSCALL_64_fastpath+0x1f/0xc2
>  RIP: resv_map_release+0x265/0x330 mm/hugetlb.c:742