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    Subject[PATCH 4.9 006/145] mm,vmscan: Make unregister_shrinker() no-op if register_shrinker() failed.
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

    commit bb422a738f6566f7439cd347d54e321e4fe92a9f upstream.

    Syzbot caught an oops at unregister_shrinker() because combination of
    commit 1d3d4437eae1bb29 ("vmscan: per-node deferred work") and fault
    injection made register_shrinker() fail and the caller of
    register_shrinker() did not check for failure.

    ----------
    [ 554.881422] FAULT_INJECTION: forcing a failure.
    [ 554.881422] name failslab, interval 1, probability 0, space 0, times 0
    [ 554.881438] CPU: 1 PID: 13231 Comm: syz-executor1 Not tainted 4.14.0-rc8+ #82
    [ 554.881443] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    [ 554.881445] Call Trace:
    [ 554.881459] dump_stack+0x194/0x257
    [ 554.881474] ? arch_local_irq_restore+0x53/0x53
    [ 554.881486] ? find_held_lock+0x35/0x1d0
    [ 554.881507] should_fail+0x8c0/0xa40
    [ 554.881522] ? fault_create_debugfs_attr+0x1f0/0x1f0
    [ 554.881537] ? check_noncircular+0x20/0x20
    [ 554.881546] ? find_next_zero_bit+0x2c/0x40
    [ 554.881560] ? ida_get_new_above+0x421/0x9d0
    [ 554.881577] ? find_held_lock+0x35/0x1d0
    [ 554.881594] ? __lock_is_held+0xb6/0x140
    [ 554.881628] ? check_same_owner+0x320/0x320
    [ 554.881634] ? lock_downgrade+0x990/0x990
    [ 554.881649] ? find_held_lock+0x35/0x1d0
    [ 554.881672] should_failslab+0xec/0x120
    [ 554.881684] __kmalloc+0x63/0x760
    [ 554.881692] ? lock_downgrade+0x990/0x990
    [ 554.881712] ? register_shrinker+0x10e/0x2d0
    [ 554.881721] ? trace_event_raw_event_module_request+0x320/0x320
    [ 554.881737] register_shrinker+0x10e/0x2d0
    [ 554.881747] ? prepare_kswapd_sleep+0x1f0/0x1f0
    [ 554.881755] ? _down_write_nest_lock+0x120/0x120
    [ 554.881765] ? memcpy+0x45/0x50
    [ 554.881785] sget_userns+0xbcd/0xe20
    (...snipped...)
    [ 554.898693] kasan: CONFIG_KASAN_INLINE enabled
    [ 554.898724] kasan: GPF could be caused by NULL-ptr deref or user memory access
    [ 554.898732] general protection fault: 0000 [#1] SMP KASAN
    [ 554.898737] Dumping ftrace buffer:
    [ 554.898741] (ftrace buffer empty)
    [ 554.898743] Modules linked in:
    [ 554.898752] CPU: 1 PID: 13231 Comm: syz-executor1 Not tainted 4.14.0-rc8+ #82
    [ 554.898755] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    [ 554.898760] task: ffff8801d1dbe5c0 task.stack: ffff8801c9e38000
    [ 554.898772] RIP: 0010:__list_del_entry_valid+0x7e/0x150
    [ 554.898775] RSP: 0018:ffff8801c9e3f108 EFLAGS: 00010246
    [ 554.898780] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
    [ 554.898784] RDX: 0000000000000000 RSI: ffff8801c53c6f98 RDI: ffff8801c53c6fa0
    [ 554.898788] RBP: ffff8801c9e3f120 R08: 1ffff100393c7d55 R09: 0000000000000004
    [ 554.898791] R10: ffff8801c9e3ef70 R11: 0000000000000000 R12: 0000000000000000
    [ 554.898795] R13: dffffc0000000000 R14: 1ffff100393c7e45 R15: ffff8801c53c6f98
    [ 554.898800] FS: 0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
    [ 554.898804] CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
    [ 554.898807] CR2: 00000000dbc23000 CR3: 00000001c7269000 CR4: 00000000001406e0
    [ 554.898813] DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000
    [ 554.898816] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
    [ 554.898818] Call Trace:
    [ 554.898828] unregister_shrinker+0x79/0x300
    [ 554.898837] ? perf_trace_mm_vmscan_writepage+0x750/0x750
    [ 554.898844] ? down_write+0x87/0x120
    [ 554.898851] ? deactivate_super+0x139/0x1b0
    [ 554.898857] ? down_read+0x150/0x150
    [ 554.898864] ? check_same_owner+0x320/0x320
    [ 554.898875] deactivate_locked_super+0x64/0xd0
    [ 554.898883] deactivate_super+0x141/0x1b0
    ----------

    Since allowing register_shrinker() callers to call unregister_shrinker()
    when register_shrinker() failed can simplify error recovery path, this
    patch makes unregister_shrinker() no-op when register_shrinker() failed.
    Also, reset shrinker->nr_deferred in case unregister_shrinker() was
    by error called twice.

    Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Signed-off-by: Aliaksei Karaliou <akaraliou.dev@gmail.com>
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Cc: Glauber Costa <glauber@scylladb.com>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    mm/vmscan.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -295,10 +295,13 @@ EXPORT_SYMBOL(register_shrinker);
    */
    void unregister_shrinker(struct shrinker *shrinker)
    {
    + if (!shrinker->nr_deferred)
    + return;
    down_write(&shrinker_rwsem);
    list_del(&shrinker->list);
    up_write(&shrinker_rwsem);
    kfree(shrinker->nr_deferred);
    + shrinker->nr_deferred = NULL;
    }
    EXPORT_SYMBOL(unregister_shrinker);


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