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From: Dmitry Vyukov <dvyukov@google.com>
Date: Mon, 9 Nov 2015 09:55:29 +0100
Message-ID: <CACT4Y+btGx7QKUjQdniRpczMof28V243Yo=Haj_G3acj0=smrg@mail.gmail.com>
Subject: WARNING in shmem_evict_inode
To: Hugh Dickins <hughd@google.com>, Andrew Morton <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Sasha Levin <sasha.levin@oracle.com>
Cc: syzkaller <syzkaller@googlegroups.com>, Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Eric Dumazet <edumazet@google.com>
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Hello,

The following program:

// autogenerated by syzkaller (http://github.com/google/syzkaller)
#include <syscall.h>
#include <string.h>
#include <stdint.h>
#include <pthread.h>

#define SYS_memfd_create 319

long fd;

void *thr(void *p)
{
        syscall(SYS_ftruncate, fd, 0x8ul, 0, 0, 0, 0);
        return 0;
}

int main()
{
        pthread_t th;

        syscall(SYS_mmap, 0x20000000ul, 0x10000ul, 0x3ul, 0x32ul,
0xfffffffffffffffful, 0x0ul);
        memcpy((void*)0x20000f96, "\x23\x65\x6d\x31\x07\x2b\x27\x29\x00", 9);
        fd = syscall(SYS_memfd_create, 0x20000f96ul, 0x2ul, 0, 0, 0, 0);
        syscall(SYS_fallocate, fd, 0x0ul, 0x31d89288ul, 0x4ul, 0, 0);
        syscall(SYS_mmap, 0x20061000ul, 0xc00000ul,
0x1a9d91e04768640bul, 0x11ul, fd, 0x0ul);
        pthread_create(&th, 0, thr, 0);
        syscall(SYS_fstat, fd, 0x20550fcful, 0, 0, 0, 0);
        pthread_join(th, 0);
        return 0;
}


triggers WARNING in shmem_evict_inode:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 10442 at mm/shmem.c:625 shmem_evict_inode+0x335/0x480()
Modules linked in:
CPU: 1 PID: 8944 Comm: executor Not tainted 4.3.0+ #39
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
 00000000ffffffff ffff88006c6afab8 ffffffff81aad406 0000000000000000
 ffff88006e39ac80 ffffffff83091660 ffff88006c6afaf8 ffffffff81100829
 ffffffff814192e5 ffffffff83091660 0000000000000271 ffff88003d075aa8
Call Trace:
 [<ffffffff81100a59>] warn_slowpath_null+0x29/0x30 kernel/panic.c:480
 [<ffffffff814192e5>] shmem_evict_inode+0x335/0x480 mm/shmem.c:625
 [<ffffffff8151560e>] evict+0x26e/0x580 fs/inode.c:542
 [<     inline     >] iput_final fs/inode.c:1477
 [<ffffffff81515f30>] iput+0x4a0/0x790 fs/inode.c:1504
 [<     inline     >] dentry_iput fs/dcache.c:358
 [<ffffffff8150667e>] __dentry_kill+0x4fe/0x700 fs/dcache.c:543
 [<     inline     >] dentry_kill fs/dcache.c:587
 [<ffffffff8150be7b>] dput+0x6ab/0x7a0 fs/dcache.c:796
 [<ffffffff814c499b>] __fput+0x3fb/0x6e0 fs/file_table.c:226
 [<ffffffff814c4d05>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8115ab23>] task_work_run+0x163/0x1f0 kernel/task_work.c:115
 [<     inline     >] exit_task_work include/linux/task_work.h:21
 [<ffffffff81105049>] do_exit+0x7f9/0x2b80 kernel/exit.c:748
 [<ffffffff8110b268>] do_group_exit+0x108/0x320 kernel/exit.c:878
 [<     inline     >] SYSC_exit_group kernel/exit.c:889
 [<ffffffff8110b49d>] SyS_exit_group+0x1d/0x20 kernel/exit.c:887
---[ end trace 43da88a03e29c2a5 ]---


Run the program in a loop, as the WARNING seems to be triggered by a race.

On commit d1e41ff11941784f469f17795a4d9425c2eb4b7a (Nov 5).
But I was also able to reproduce it on a 3.11-based kernel.
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