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    Subject[PATCH 5.15 400/530] fs: dlm: fix race in lowcomms
    Date
    From: Alexander Aring <aahringo@redhat.com>

    [ Upstream commit 30ea3257e8766027c4d8d609dcbd256ff9a76073 ]

    This patch fixes a race between queue_work() in
    _dlm_lowcomms_commit_msg() and srcu_read_unlock(). The queue_work() can
    take the final reference of a dlm_msg and so msg->idx can contain
    garbage which is signaled by the following warning:

    [ 676.237050] ------------[ cut here ]------------
    [ 676.237052] WARNING: CPU: 0 PID: 1060 at include/linux/srcu.h:189 dlm_lowcomms_commit_msg+0x41/0x50
    [ 676.238945] Modules linked in: dlm_locktorture torture rpcsec_gss_krb5 intel_rapl_msr intel_rapl_common iTCO_wdt iTCO_vendor_support qxl kvm_intel drm_ttm_helper vmw_vsock_virtio_transport kvm vmw_vsock_virtio_transport_common ttm irqbypass crc32_pclmul joydev crc32c_intel serio_raw drm_kms_helper vsock virtio_scsi virtio_console virtio_balloon snd_pcm drm syscopyarea sysfillrect sysimgblt snd_timer fb_sys_fops i2c_i801 lpc_ich snd i2c_smbus soundcore pcspkr
    [ 676.244227] CPU: 0 PID: 1060 Comm: lock_torture_wr Not tainted 5.19.0-rc3+ #1546
    [ 676.245216] Hardware name: Red Hat KVM/RHEL-AV, BIOS 1.16.0-2.module+el8.7.0+15506+033991b0 04/01/2014
    [ 676.246460] RIP: 0010:dlm_lowcomms_commit_msg+0x41/0x50
    [ 676.247132] Code: fe ff ff ff 75 24 48 c7 c6 bd 0f 49 bb 48 c7 c7 38 7c 01 bd e8 00 e7 ca ff 89 de 48 c7 c7 60 78 01 bd e8 42 3d cd ff 5b 5d c3 <0f> 0b eb d8 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48
    [ 676.249253] RSP: 0018:ffffa401c18ffc68 EFLAGS: 00010282
    [ 676.249855] RAX: 0000000000000001 RBX: 00000000ffff8b76 RCX: 0000000000000006
    [ 676.250713] RDX: 0000000000000000 RSI: ffffffffbccf3a10 RDI: ffffffffbcc7b62e
    [ 676.251610] RBP: ffffa401c18ffc70 R08: 0000000000000001 R09: 0000000000000001
    [ 676.252481] R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000005
    [ 676.253421] R13: ffff8b76786ec370 R14: ffff8b76786ec370 R15: ffff8b76786ec480
    [ 676.254257] FS: 0000000000000000(0000) GS:ffff8b7777800000(0000) knlGS:0000000000000000
    [ 676.255239] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    [ 676.255897] CR2: 00005590205d88b8 CR3: 000000017656c003 CR4: 0000000000770ee0
    [ 676.256734] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    [ 676.257567] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    [ 676.258397] PKRU: 55555554
    [ 676.258729] Call Trace:
    [ 676.259063] <TASK>
    [ 676.259354] dlm_midcomms_commit_mhandle+0xcc/0x110
    [ 676.259964] queue_bast+0x8b/0xb0
    [ 676.260423] grant_pending_locks+0x166/0x1b0
    [ 676.261007] _unlock_lock+0x75/0x90
    [ 676.261469] unlock_lock.isra.57+0x62/0xa0
    [ 676.262009] dlm_unlock+0x21e/0x330
    [ 676.262457] ? lock_torture_stats+0x80/0x80 [dlm_locktorture]
    [ 676.263183] torture_unlock+0x5a/0x90 [dlm_locktorture]
    [ 676.263815] ? preempt_count_sub+0xba/0x100
    [ 676.264361] ? complete+0x1d/0x60
    [ 676.264777] lock_torture_writer+0xb8/0x150 [dlm_locktorture]
    [ 676.265555] kthread+0x10a/0x130
    [ 676.266007] ? kthread_complete_and_exit+0x20/0x20
    [ 676.266616] ret_from_fork+0x22/0x30
    [ 676.267097] </TASK>
    [ 676.267381] irq event stamp: 9579855
    [ 676.267824] hardirqs last enabled at (9579863): [<ffffffffbb14e6f8>] __up_console_sem+0x58/0x60
    [ 676.268896] hardirqs last disabled at (9579872): [<ffffffffbb14e6dd>] __up_console_sem+0x3d/0x60
    [ 676.270008] softirqs last enabled at (9579798): [<ffffffffbc200349>] __do_softirq+0x349/0x4c7
    [ 676.271438] softirqs last disabled at (9579897): [<ffffffffbb0d54c0>] irq_exit_rcu+0xb0/0xf0
    [ 676.272796] ---[ end trace 0000000000000000 ]---

    I reproduced this warning with dlm_locktorture test which is currently
    not upstream. However this patch fix the issue by make a additional
    refcount between dlm_lowcomms_new_msg() and dlm_lowcomms_commit_msg().
    In case of the race the kref_put() in dlm_lowcomms_commit_msg() will be
    the final put.

    Signed-off-by: Alexander Aring <aahringo@redhat.com>
    Signed-off-by: David Teigland <teigland@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/dlm/lowcomms.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
    index b11f695261f5..9d7078a1dc8b 100644
    --- a/fs/dlm/lowcomms.c
    +++ b/fs/dlm/lowcomms.c
    @@ -1319,6 +1319,8 @@ struct dlm_msg *dlm_lowcomms_new_msg(int nodeid, int len, gfp_t allocation,
    return NULL;
    }

    + /* for dlm_lowcomms_commit_msg() */
    + kref_get(&msg->ref);
    /* we assume if successful commit must called */
    msg->idx = idx;
    return msg;
    @@ -1353,6 +1355,8 @@ void dlm_lowcomms_commit_msg(struct dlm_msg *msg)
    {
    _dlm_lowcomms_commit_msg(msg);
    srcu_read_unlock(&connections_srcu, msg->idx);
    + /* because dlm_lowcomms_new_msg() */
    + kref_put(&msg->ref, dlm_msg_release);
    }

    void dlm_lowcomms_put_msg(struct dlm_msg *msg)
    --
    2.35.1


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