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charset="iso-8859-1" Content-ID: <30DDB4AB0E019349A68623B9F1161EF5@eurprd04.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: silk.us X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: AM6PR04MB5639.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3d96fb74-d202-4b96-001c-08d92e663ef8 X-MS-Exchange-CrossTenant-originalarrivaltime: 13 Jun 2021 12:24:52.6328 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 4a3c5477-cb0e-470b-aba6-13bd9debb76b X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 2N/0itK6O0YLE7i3LnD0WNmimS/ReG29bZ4dSnPGR7owBAwMCR46R0xfi6H8TwOPOSTYJr2717uL4IcOq03SiA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM7PR04MB7016 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hi *, Under a very high load of io traffic, we got the below=A0 BUG trace. We can see that: plist_for_each_entry_safe(this, next,=A0&hb1->chain, list) { =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 if (match_futex (&this->key, = &key1)) =A0 were called with hb1 =3D NULL at futex_wake_up function. And there is no protection on the code regarding such a scenario. =A0 The NULL can=A0 be geting from: hb1 =3D hash_futex(&key1); =A0 How can we protect against such a situation? =A0 =A0 =A0 Deatailes below: =A0 =A0 un 10 20:49:40 c-node04 kernel: [97562.144447] STAR4BLKS0_WORK[12672]: segf= ault at 1aa7cba6 ip 00007f924a6bc68c sp 00007f6ca92e1b70 error 15 Jun 10 20:49:40 c-node04 kram: rpoll(0x23396f70, 24, 50) returning 0 times:= 0, 0, 0, 2180, 0 ccount 104 Jun 10 20:49:40 c-node04 kernel: [97562.144463] BUG: unable to handle kerne= l NULL pointer dereference at 0000000000000246 Jun 10 20:49:40 c-node04 kernel: [97562.145450] PGD 2012ee4067 P4D 2012ee40= 67 PUD 20135a0067 PMD 0 Jun 10 20:49:40 c-node04 kernel: [97562.145450] Oops: 0000 [#1] SMP Jun 10 20:49:40 c-node04 kernel: [97562.145450] CPU: 36 PID: 12668 Comm: ST= AR4BLKS0_WORK Kdump: loaded Tainted: G=A0=A0=A0=A0=A0=A0=A0 W=A0 OE=A0=A0= =A0=A0 4.19.149-KM6 #1 Jun 10 20:49:40 c-node04 kram: rpoll(0x7fe624135b90, 85, 50) returning 0 ti= mes: 0, 0, 0, 2203, 0 ccount 42 Jun 10 20:49:40 c-node04 kernel: [97562.145450] Hardware name: Microsoft Co= rporation Virtual Machine/Virtual Machine, BIOS 090008=A0 12/07/2018 Jun 10 20:49:40 c-node04 kernel: [97562.145450] RIP: 0010:do_futex+0xdf/0xa= 90 Jun 10 20:49:40 c-node04 kernel: [97562.145450] Code: 08 4c 8d 6d 08 48 8b = 3a 48 8d 72 e8 49 39 d5 4c 8d 67 e8 0f 84 89 00 00 00 31 c0 44 89 3c 24 41 = 89 df 44 89 f3 41 89 c6 eb 16 <49> 8b 7c 24 18 49 8d 54 24 18 4c 89 e6 4c 39 ea 4c 8d 67 e8 74 58 Jun 10 20:49:40 c-node04 kernel: [97562.145450] RSP: 0018:ffff97f6ea8bbdf0 = EFLAGS: 00010283 Jun 10 20:49:40 c-node04 kernel: [97562.145450] RAX: 00007f6db1a5d000 RBX: = 0000000000000001 RCX: ffffa5530c5f0140 Jun 10 20:49:40 c-node04 kernel: [97562.145450] RDX: ffff97f6e4287d58 RSI: = ffff97f6e4287d40=A0RDI: 0000000000000246 Jun 10 20:49:40 c-node04 kram: rpoll(0x7fe62414a860, 2, 50) returning 0 tim= es: 0, 0, 0, 2191, 0 ccount 277 Jun 10 20:49:40 c-node04 kernel: [97562.145450] RBP: ffffa5530c5bd580 R08: = 00007f6db1a5d9c0 R09: 0000000000000001 Jun 10 20:49:40 c-node04 kernel: [97562.145450] R10: 0000000004000001 R11: = 0000000000000000 R12: 000000000000022e Jun 10 20:49:40 c-node04 kernel: [97562.145450] R13: ffffa5530c5bd588 R14: = 0000000000000000 R15: 0000000000000000 Jun 10 20:49:40 c-node04 kernel: [97562.145450] FS:=A0 00007f6cab2e6700(000= 0) GS:ffff98339f500000(0000) knlGS:0000000000000000 Jun 10 20:49:40 c-node04 kernel: [97562.145450] CS:=A0 0010 DS: 0000 ES: 00= 00 CR0: 0000000080050033 Jun 10 20:49:40 c-node04 kernel: [97562.145450] CR2: 0000000000000246 CR3: = 00000020168d3003 CR4: 00000000003606e0 Jun 10 20:49:40 c-node04 kernel: [97562.145450] DR0: 0000000000000000 DR1: = 0000000000000000 DR2: 0000000000000000 Jun 10 20:49:40 c-node04 kernel: [97562.145450] DR3: 0000000000000000 DR6: = 00000000fffe0ff0 DR7: 0000000000000400 Jun 10 20:49:40 c-node04 kernel: [97562.145450] Call Trace: Jun 10 20:49:40 c-node04 kernel: [97562.145450]=A0 ? plist_add+0xc1/0xf0 Jun 10 20:49:40 c-node04 kernel: [97562.145450]=A0 __x64_sys_futex+0x143/0x= 1 Jun 10 20:49:40 c-node04 kernel: [97562.145450]=A0 do_syscall_64+0x59/0x1b0 Jun 10 20:49:40 c-node04 kernel: [97562.145450]=A0 ? prepare_exit_to_usermo= de+0x70/0x90 Jun 10 20:49:40 c-node04 kram: rpoll(0x233a2b50, 1, 50) returning 0 times: = 0, 0, 0, 2177, 0 ccount 277 Jun 10 20:49:40 c-node04 kernel: [97562.145450]=A0 entry_SYSCALL_64_after_h= wframe+0x44/0xa9 Jun 10 20:49:40 c-node04 kram: rpoll(0x7f914813d480, 90, 50) returning 0 ti= mes: 0, 0, 0, 2166, 0 ccount 35 Jun 10 20:49:40 c-node04 kernel: [97562.145450] RIP: 0033:0x7f924a6bcf28 Jun 10 20:49:40 c-node04 kernel: [97562.145450] Code: 74 1a 49 8b 48 20 44 = 8b 59 10 41 83 e3 30 41 83 fb 20 74 21 64 0b 34 25 48 00 00 00 41 ba 01 00 = 00 00 41 b9 01 00 00 04 0f 05 <48> 3d 01 f0 ff ff 73 1f 31 c0 c3 be 8c 00 0= 0 00 49 89 c8 4d 31 d2 =A0 =A0 =A0 RIP: 0010:do_futex+0xdf/0xa90 =A0 0xffffffff81138eff is in do_futex (kernel/futex.c:1748). 1743=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 put_futex_key(&key1); 1744=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 cond_resched(); 1745=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 goto retry; 1746=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 } 1747=A0=A0=A0=A0=A0=A0 1748=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 plis= t_for_each_entry_safe(this, next, &hb1->chain, list) { 1749=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 if (match_futex (&this->key, = &key1)) { 1750=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0 if (this->pi_state || this->rt_waiter) { 1751=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 ret =3D = -EINVAL; 1752=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 goto out= _unlock; (gdb) =A0 =A0 =A0 plist_for_each_entry_safe(this, next, &hb1->chain, list) { =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 if (match_futex (&this->key, = &key1)) { =A0 =A0 =A0 =A0 This happened in kernel=A0 4.19.149 running on Azure vm =A0 =A0 Thx David Reply=20 Forward=20 MO