[LU-17174] lustre hashes broken now.

• Type: Bug
• Resolution: Fixed
• Priority: Blocker
• Fix Version/s: Lustre 2.16.0
• Severity: 3
• Assignee: Alexey Lyashkov
• Reporter: Alexey Lyashkov

Description

lustre hash functions broken now after landing
commit 239e826876e5e20405e14a180a8fd4377d6553b2
Author: Timothy Day <[e-mail]>
Date: Mon Feb 6 20:02:15 2023 +0000

LU-16518 misc: use fixed hash code.

static __always_inline u32 cfs_hash_64(u64 val, unsigned int bits)
{
#if BITS_PER_LONG == 64
        / 64x64-bit multiply is efficient on all 64-bit processors /
        return val * GOLDEN_RATIO_64 >> (64 - bits);
#else
        / Hash 64 bits using only 32x32-bit multiply. /
        return cfs_hash_32(((u32)val ^ ((val >> 32) * GOLDEN_RATIO_32)), bits);
#endif
}

 static unsigned
 ldlm_export_flock_hash(struct cfs_hash hs, const void key, unsigned mask)
 {
-       return cfs_hash_u64_hash(*(__u64 *)key, mask);
+       return cfs_hash_64(*(__u64 *)key, 0) & mask;
 }

this change means we have shift for 64bits for any result, it caused a return zero/0xfffff... at any input and warning with debug kernel.

[10939.945272] ================================================================================
[10939.946792] UBSAN: Undefined behaviour in include/linux/hash.h:81:31
[10939.948193] shift exponent 64 is too large for 64-bit type 'long long unsigned int'
[10939.949869] CPU: 2 PID: 384127 Comm: ll_mgs_0002 Tainted: G    B   W  OE    ---------r-  - 4.18.0-305.25.1.el8_4.x86_64+debug #1
[10939.952333] Hardware name: Red Hat KVM/RHEL-AV, BIOS 1.16.0-3.module_el8.7.0+3346+68867adb 04/01/2014
[10939.954274] Call Trace:
[10939.954823]  dump_stack+0x8e/0xd0
[10939.955543]  ubsan_epilogue+0x5/0x21
[10939.956329]  __ubsan_handle_shift_out_of_bounds.cold.13+0x14/0x98
[10939.957581]  ? rcu_read_unlock+0x50/0x50
[10939.958418]  ? lock_acquired+0x6c6/0xe60
[10939.959367]  ? lprocfs_stats_lock+0x15d/0x1b0 [obdclass]
[10939.960699]  ldlm_export_lock_hash+0x49/0x4d [ptlrpc]
[10939.961715]  cfs_hash_bd_from_key+0x88/0x2e0 [libcfs]
[10939.962821]  cfs_hash_add+0xef/0xb60 [libcfs]
[10939.963830]  ? class_handle_hash+0x274/0x5f0 [obdclass]
[10939.964961]  ? cfs_hash_rehash+0x7a0/0x7a0 [libcfs]
[10939.966167]  ? ldlm_lock_create+0x734/0x1e20 [ptlrpc]
[10939.967287]  ldlm_handle_enqueue+0x8dc/0x48e0 [ptlrpc]
[10939.968352]  ? do_raw_spin_unlock+0x14b/0x230
[10939.969377]  ? ldlm_setup+0x1af0/0x1af0 [ptlrpc]
[10939.970509]  ? __req_capsule_get+0x7ff/0x11f0 [ptlrpc]
[10939.971710]  ? lustre_swab_ldlm_lock_desc+0x230/0x230 [ptlrpc]
[10939.972973]  tgt_enqueue+0x148/0x5a0 [ptlrpc]
[10939.974139]  tgt_request_handle+0x179c/0x3ff0 [ptlrpc]
[10939.975403]  ? tgt_brw_write+0x5a00/0x5a00 [ptlrpc]
[10939.976594]  ptlrpc_server_handle_request+0xa34/0x1f50 [ptlrpc]
[10939.977936]  ? lu_context_exit+0x15a/0x2c0 [obdclass]
[10939.979045]  ptlrpc_main+0x1ae0/0x2f40 [ptlrpc]
[10939.980062]  ? __kthread_parkme+0xc4/0x190
[10939.981068]  ? ptlrpc_wait_event+0xf40/0xf40 [ptlrpc]
[10939.982107]  kthread+0x344/0x410
[10939.982811]  ? kthread_insert_work_sanity_check+0xd0/0xd0
[10939.983941]  ret_from_fork+0x3a/0x50
[10939.984776] ================================================================================

Issue Links

• is related to: LU-17680 performance regression in sanity test_123ac