fs: WARNING in locks_free_lock_context()

[Dmitry Vyukov]

Hello,

The following program triggers
WARN_ON_ONCE(!list_empty(&ctx->flc_posix)) warning in
locks_free_lock_context (run it in a loop):

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

#ifndef SYS_memfd_create
#define SYS_memfd_create 319
#endif

long r[15];
long done[14];

void *thr(void *arg)
{
        if (rand()%2)
                usleep(100);

        switch ((long)arg) {
        case 0:
                r[0] = syscall(SYS_mmap, 0x20000000ul, 0x5000ul,
0x3ul, 0x32ul, 0xfffffffffffffffful, 0x0ul);
                break;
        case 1:
                memcpy((void*)0x20000c49,
"\xb6\x70\x70\x70\x31\x73\x65\x63\x75\x72\x69\x74\x79\x9e\x00", 15);
                r[2] = syscall(SYS_memfd_create, 0x20000c49ul, 0x3ul,
0, 0, 0, 0);
                break;
        case 2:
                r[3] = syscall(SYS_socketpair, 0x1ul, 0x1ul, 0x0ul,
0x20001000ul, 0, 0);
                if (r[3] != -1)
                                r[4] = *(uint32_t*)0x20001000;
                if (r[3] != -1)
                                r[5] = *(uint32_t*)0x20001004;
                break;
        case 3:
                *(uint16_t*)0x20000000 = (uint16_t)0x0;
                *(uint16_t*)0x20000002 = (uint16_t)0x1;
                *(uint64_t*)0x20000008 = (uint64_t)0x6;
                *(uint64_t*)0x20000010 = (uint64_t)0xad;
                *(uint32_t*)0x20000018 = (uint32_t)0x0;
                r[11] = syscall(SYS_fcntl, r[5], 0x7ul, 0x20000000ul, 0, 0, 0);
                break;
        case 4:
                r[12] = syscall(SYS_write, r[5], 0x200006cbul,
0x1000ul, 0, 0, 0);
                break;
        case 5:
                r[13] = syscall(SYS_close, r[5], 0, 0, 0, 0, 0);
                break;
        case 6:
                r[14] = syscall(SYS_dup2, r[2], r[4], 0, 0, 0, 0);
                break;
        }
        done[(long)arg] = 1;
        return 0;
}

int main()
{
        long i, j;
        pthread_t th[14];

        srand(time(0)+getpid());
        memset(r, -1, sizeof(r));
        for (i = 0; i < 7; i++) {
                pthread_create(&th[i], 0, thr, (void*)i);
                for (j = 0; j < 10; j++) {
                        if (done[i])
                                break;
                        usleep(100);
                }
        }
        for (i = 0; i < 7; i++)
                done[i] = 0;
        for (i = 0; i < 7; i++) {
                pthread_create(&th[7+i], 0, thr, (void*)i);
                if (rand()%2)
                        continue;
                for (j = 0; j < 10; j++) {
                        if (done[i])
                                break;
                        usleep(100);
                }
        }
        usleep(100);
        return 0;
}


------------[ cut here ]------------
WARNING: CPU: 3 PID: 1975 at fs/locks.c:241
locks_free_lock_context+0x118/0x180()
Modules linked in:
CPU: 3 PID: 1975 Comm: a.out Not tainted 4.4.0-rc6+ #173
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
 00000000ffffffff ffff880068e67bf8 ffffffff82899ffd 0000000000000000
 ffff88006130af00 ffffffff85e17d60 ffff880068e67c38 ffffffff812ebbb9
 ffffffff818162d8 ffffffff85e17d60 00000000000000f1 ffff8800685c2828
Call Trace:
 [<     inline     >] __dump_stack lib/dump_stack.c:15
 [<ffffffff82899ffd>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
 [<ffffffff812ebbb9>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:460
 [<ffffffff812ebde9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:493
 [<ffffffff818162d8>] locks_free_lock_context+0x118/0x180 fs/locks.c:241
 [<ffffffff81765783>] __destroy_inode+0x1d3/0x4d0 fs/inode.c:228
 [<ffffffff81765acb>] destroy_inode+0x4b/0x120 fs/inode.c:253
 [<ffffffff81765ec0>] evict+0x320/0x4f0 fs/inode.c:559
 [<     inline     >] iput_final fs/inode.c:1477
 [<ffffffff817665dc>] iput+0x45c/0x850 fs/inode.c:1504
 [<     inline     >] dentry_iput fs/dcache.c:358
 [<ffffffff81757237>] __dentry_kill+0x457/0x620 fs/dcache.c:543
 [<     inline     >] dentry_kill fs/dcache.c:587
 [<ffffffff8175c499>] dput+0x659/0x740 fs/dcache.c:796
 [<ffffffff817162fc>] __fput+0x42c/0x780 fs/file_table.c:226
 [<ffffffff817166d5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8134679b>] task_work_run+0x16b/0x200 kernel/task_work.c:115
 [<     inline     >] tracehook_notify_resume include/linux/tracehook.h:191
 [<ffffffff81003990>] exit_to_usermode_loop+0x180/0x1a0
arch/x86/entry/common.c:251
 [<     inline     >] prepare_exit_to_usermode arch/x86/entry/common.c:282
 [<ffffffff8100631f>] syscall_return_slowpath+0x19f/0x210
arch/x86/entry/common.c:344
 [<ffffffff85ccea22>] int_ret_from_sys_call+0x25/0x9f
arch/x86/entry/entry_64.S:281
---[ end trace 2dde0624dd974a19 ]---


On commit 4ef7675344d687a0ef5b0d7c0cee12da005870c0 (Dec 20).
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