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adobriyan@gmail.com, jack@suse.cz, viro@zeniv.linux.org.uk, Sebastian Andrzej Siewior , Thomas Gleixner Subject: context switch within RCU read-side critical section in next-20260518+ with PREEMPT_RT Date: Thu, 21 May 2026 00:52:44 +0200 Message-ID: <20260520225245.2962-1-spasswolf@web.de> X-Mailer: git-send-email 2.47.3 In-Reply-To: 20260425220844.1763933-3-mjguzik@gmail.com References: Precedence: bulk X-Mailing-List: linux-next@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:z+O7qBU6cfTshuykKGyEqRUFHr8Rcq7z1D0NqR+6f4MuDQmYqSF 1aNQOQ+Nq+X1VpI/IK7rpla5EgXMIhc3JviSKXr/erTknsL2AmHgSg45gV8bbsa9xwbvNLi dAhYDxy1ttSW5cyc/3zBzZzvMxxjM7HJeDj56xZRC3jREZGarXIrjoSYKl5HeEP0O109QXI Qqlo9drHfoLFGkHLs920Q== X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:jS1Ca1t03y0=;pq0rqvVI8DyLCB+7QJ76mgyrCqY HmS4DH/ko5i0SSl+03PVEzO8bRZxrJ2ThvusveryiDyBu1ghJqzzkSvSHz0gOKqLG7TTpTeI3 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displaying the following error message. A= fter about ~1min booting continues to a rescue shell where I could save the dmesg output (Th= e output shown=20 here is not from next-20260519 but from a step in the bisection). [ 2.900440] [ T709] ------------[ cut here ]------------ [ 2.900441] [ T709] Voluntary context switch within RCU read-side cri= tical section! [ 2.900441] [ T709] WARNING: kernel/rcu/tree_plugin.h:332 at rcu_note= _context_switch+0x2ac/0x460, CPU#4: systemd-fstab-g/709 [ 2.900447] [ T709] Modules linked in: efivarfs autofs4 ext4 mbcache = jbd2 hid_generic usbhid hid amdgpu drm_client_lib i2c_algo_bit drm_buddy dr= m_ttm_helper ttm drm_exec drm_suballoc_helper mfd_core drm_panel_backlight_= quirks gpu_sched xhci_pci amdxcp drm_display_helper xhci_hcd drm_kms_helper= ahci libahci drm libata usbcore nvme scsi_mod nvme_core igc video i2c_piix= 4 cec nvme_keyring i2c_smbus usb_common scsi_common crc16 nvme_auth wmi gpi= o_amdpt gpio_generic [ 2.900456] [ T709] CPU: 4 UID: 0 PID: 709 Comm: systemd-fstab-g Not = tainted 7.1.0-rc4-bisect-02057-g134bedf6b3e5 #452 PREEMPT_RT=20 [ 2.900457] [ T709] Hardware name: ASUS System Product Name/ROG STRIX= B850-F GAMING WIFI, BIOS 1627 02/05/2026 [ 2.900458] [ T709] RIP: 0010:rcu_note_context_switch+0x2ac/0x460 [ 2.900459] [ T709] Code: ef e8 58 56 87 00 48 8b 55 28 b9 01 00 00 0= 0 4c 89 ef c6 45 11 00 48 89 c6 e8 e0 99 ff ff e9 cd fd ff ff 48 8d 3d 84 8= a de 00 <67> 48 0f b9 3a e9 89 fd ff ff a9 a0 20 00 00 0f 85 df 00 00 00 f6 [ 2.900460] [ T709] RSP: 0018:ffffb538c1e3fb98 EFLAGS: 00010002 [ 2.900461] [ T709] RAX: 0000000000000001 RBX: ffff9bd494a0db00 RCX: = 0000000000000000 [ 2.900462] [ T709] RDX: 0000000000000000 RSI: ffffffffb27ad182 RDI: = ffffffffb2d29400 [ 2.900462] [ T709] RBP: ffff9be33f326b00 R08: ffffeba64492bec0 R09: = ffff9bd491ed1100 [ 2.900462] [ T709] R10: 0000000000000001 R11: ffffeba64492bec0 R12: = 0000000000000000 [ 2.900462] [ T709] R13: 0000000000000000 R14: ffff9bd494a0db00 R15: = ffffb538c1e3fcc0 [ 2.900463] [ T709] FS: 00007f0367aaf9c0(0000) GS:ffff9be38c475000(0= 000) knlGS:0000000000000000 [ 2.900464] [ T709] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 2.900464] [ T709] CR2: 00007f082baae1d4 CR3: 0000000111ff2000 CR4: = 0000000000f50ef0 [ 2.900464] [ T709] PKRU: 55555554 [ 2.900465] [ T709] Call Trace: [ 2.900466] [ T709] [ 2.900466] [ T709] ? __schedule+0x78/0xe50 [ 2.900469] [ T709] ? blk_finish_plug+0x23/0x40 [ 2.900472] [ T709] ? read_pages+0x17f/0x210 [ 2.900474] [ T709] ? schedule+0x22/0xd0 [ 2.900475] [ T709] ? io_schedule+0x41/0x60 [ 2.900476] [ T709] ? folio_wait_bit_common+0x10d/0x2f0 [ 2.900477] [ T709] ? filemap_invalidate_unlock_two+0x40/0x40 [ 2.900478] [ T709] ? filemap_fault+0x7a1/0xfc0 [ 2.900479] [ T709] ? __do_fault+0x30/0x90 [ 2.900480] [ T709] ? do_fault+0x3a9/0x5a0 [ 2.900481] [ T709] ? __handle_mm_fault+0x2c6/0x3a0 [ 2.900482] [ T709] ? handle_mm_fault+0xdc/0x2c0 [ 2.900483] [ T709] ? do_user_addr_fault+0x1e2/0x5f0 [ 2.900485] [ T709] ? exc_page_fault+0x49/0x70 [ 2.900486] [ T709] ? asm_exc_page_fault+0x26/0x30 [ 2.900487] [ T709] [ 2.900487] [ T709] ---[ end trace 0000000000000000 ]--- I bisected the error from v7.1-rc4 to next-20260519, declaring a commit as GOOD when it survives 12 boots without displaying this error: 7.1.0-rc4-bisect-03214-ge373a2ca9f8f error on 5th boot BAD 7.1.0-rc4-bisect-01608-gbd4178634082 12 boots without error GOOD 7.1.0-rc4-bisect-02426-g6491cb7030d4 error on 2nd boot BAD 7.1.0-rc4-bisect-02025-gd97e5246790d 12 boots without error GOOD 7.1.0-rc1-bisect-00173-gd97d13c24d78 12 boots without error GOOD 7.1.0-rc4-bisect-02116-g44f7bcae0b3d error on 6th boot BAD 7.1.0-rc4-bisect-00045-g0a8e31d303d5 12 boots without error GOOD 7.0.0-bisect-10592-g2acc3b265f94 12 boots without error GOOD 7.1.0-rc4-bisect-02057-g134bedf6b3e5 error on 1st boot BAD 7.0.0-bisect-10570-g99bde1dfe878 12 boots without error GOOD 7.0.0-bisect-10616-g5d1aae9252b4 12 boots without error GOOD 7.1.0-rc4-bisect-00003-g24214ad405d1 12 boots without error GOOD 7.1.0-rc4-bisect-02055-g95185f3a36ec error on 4th boot BAD This first bisect gives this bogus result: commit 95185f3a36ec ("Merge branch 'for-next' of https://git.kernel.org/pub= /scm/linux/kernel/git/hid/hid.git") which shows there's a false negative in the bisection above. So I retested some of the commits from above: 7.1.0-rc4-bisect-02025-gd97e5246790d error on 1st boot (13 boots in total)= BAD 7.1.0-rc4-bisect-01608-gbd4178634082 12 boots without error (25 in total) = GOOD and started a bisection from bd4178634082 to d97e5246790d (with increased number of boots required for a good commit) 7.1.0-rc4-bisect-00204-g43467cbc2260 18 boots without error GOOD 7.1.0-rc4-bisect-00333-geda8cb3fb0cb error on 3rd boot BAD With the good and bad commits this close I took a look at git log --oneline 43467cbc2260..eda8cb3fb0cb and found exactly one RCU related commit: dc651e25a6d2 ("fs: RCU-ify filesystems list") So I reverted the this commit in next-20260519 (to get a clean revert I nee= ded to revert commit 36b3306779ea ("fs: cache the string generated by reading /proc/filesystems"= ) first. $ git log --oneline c7321982a5d0 (HEAD -> rcu_critical_readside_bug) Revert "fs: RCU-ify filesy= stems list" 16ff8d6e7c28 Revert "fs: cache the string generated by reading /proc/filesy= stems" 6a50ba100ace (tag: next-20260519, origin/master, origin/HEAD, master) Add l= inux-next specific files for 20260519 With these reverts next-20260519 boots 30 times in a row without error, so it appears that commit dc651e25a6d2 ("fs: RCU-ify filesystems list") causin= g the error. To see if this issue is PREEMPT_RT only I also tested next-20260519 *withou= t* PREEMPT_RT and got a different bug at my first boot (the second boot worked, the third= failed again) In the non-RT case there's no rescue shell so this error message is copied = from a (bad) photo: [ 2.823291][ T510] BUG: scheduling while atomic: sytemd-hiberna/510 [ 2.824837][ T504] /usr/lib/systemd/system-generators/systemd-hibernate-res= ume-generator terminated by signal SEGV BUG: scheduling while atomic: sytemd-hiberna/510 Call Trace: dump_stack_lvl __schedule_bug.cold [...] asm_exc_page_fault Code: unable to access opcode bytes at 0x7f243337e216 To see if the non-RT error is caused by the same commit as the RT error I t= ested next-20260519 with the reverts and *without* PREEMPT_RT. With the reverts t= here was no error in 20 boots. So the problem in the non-RT and RT case seem to be c= aused by the same commits. Hardware used: $ cat /proc/cpuinfo processor : 31 vendor_id : AuthenticAMD cpu family : 26 model : 68 model name : AMD Ryzen 9 9950X 16-Core Processor stepping : 0 microcode : 0xb404035 cpu MHz : 624.194 cache size : 1024 KB physical id : 0 siblings : 32 core id : 15 cpu cores : 16 apicid : 31 initial apicid : 31 fpu : yes fpu_exception : yes cpuid level : 16 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat = pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtsc= p lm constant_tsc rep_good amd_lbr_v2 nopl xtopology nonstop_tsc cpuid extd= _apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 = movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_l= egacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce topoext p= erfctr_core perfctr_nb bpext perfctr_llc mwaitx cpuid_fault cpb cat_l3 cdp_= l3 hw_pstate ssbd mba perfmon_v2 ibrs ibpb stibp ibrs_enhanced vmmcall fsgs= base tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a avx512f avx512dq= rdseed adx smap avx512ifma clflushopt clwb avx512cd sha_ni avx512bw avx512= vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_m= bm_local user_shstk avx_vnni avx512_bf16 clzero irperf xsaveerptr rdpru wbn= oinvd cppc arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasi= d decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif x2avic v_= spec_ctrl vnmi avx512vbmi umip pku ospke avx512_vbmi2 gfni vaes vpclmulqdq = avx512_vnni avx512_bitalg avx512_vpopcntdq rdpid bus_lock_detect movdiri mo= vdir64b overflow_recov succor smca fsrm avx512_vp2intersect flush_l1d amd_l= br_pmc_freeze bugs : sysret_ss_attrs spectre_v1 spectre_v2 spec_store_bypass srso spectr= e_v2_user vmscape bogomips : 8599.98 TLB size : 192 4K pages clflush size : 64 cache_alignment : 64 address sizes : 48 bits physical, 48 bits virtual power management: ts ttp tm hwpstate cpb eff_freq_ro [13] [14] $ lspci -nn 00:00.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Root Complex [1022:14d8] 00:00.2 IOMMU [0806]: Advanced Micro Devices, Inc. [AMD] Raphael/Granite Ri= dge IOMMU [1022:14d9] 00:01.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Dummy Host Bridge [1022:14da] 00:01.1 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Raphael/Grani= te Ridge GPP Bridge [1022:14db] 00:01.2 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Raphael/Grani= te Ridge GPP Bridge [1022:14db] 00:02.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Dummy Host Bridge [1022:14da] 00:02.1 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Raphael/Grani= te Ridge GPP Bridge [1022:14db] 00:03.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Dummy Host Bridge [1022:14da] 00:04.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Dummy Host Bridge [1022:14da] 00:08.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Dummy Host Bridge [1022:14da] 00:08.1 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Raphael/Grani= te Ridge Internal GPP Bridge to Bus [C:A] [1022:14dd] 00:08.3 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Raphael/Grani= te Ridge Internal GPP Bridge to Bus [C:A] [1022:14dd] 00:14.0 SMBus [0c05]: Advanced Micro Devices, Inc. [AMD] FCH SMBus Controll= er [1022:790b] (rev 71) 00:14.3 ISA bridge [0601]: Advanced Micro Devices, Inc. [AMD] FCH LPC Bridg= e [1022:790e] (rev 51) 00:18.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Data Fabric; Function 0 [1022:14e0] 00:18.1 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Data Fabric; Function 1 [1022:14e1] 00:18.2 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Data Fabric; Function 2 [1022:14e2] 00:18.3 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Data Fabric; Function 3 [1022:14e3] 00:18.4 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Data Fabric; Function 4 [1022:14e4] 00:18.5 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Data Fabric; Function 5 [1022:14e5] 00:18.6 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Data Fabric; Function 6 [1022:14e6] 00:18.7 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Raphael/Gran= ite Ridge Data Fabric; Function 7 [1022:14e7] 01:00.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD/ATI] Navi 10 X= L Upstream Port of PCI Express Switch [1002:1478] (rev 25) 02:00.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD/ATI] Navi 10 X= L Downstream Port of PCI Express Switch [1002:1479] (rev 25) 03:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD= /ATI] Navi 44 [RX 9060 XT] [1002:7590] (rev c0) 03:00.1 Audio device [0403]: Advanced Micro Devices, Inc. [AMD/ATI] Navi 48= HDMI/DP Audio Controller [1002:ab40] 04:00.0 Non-Volatile memory controller [0108]: Samsung Electronics Co Ltd N= VMe SSD 9100 PRO [PM9E1] [144d:a810] 05:00.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 600 Series Ch= ipset PCIe Switch Upstream Port [1022:43f4] (rev 01) 06:00.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 600 Series Ch= ipset PCIe Switch Downstream Port [1022:43f5] (rev 01) 06:06.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 600 Series Ch= ipset PCIe Switch Downstream Port [1022:43f5] (rev 01) 06:07.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 600 Series Ch= ipset PCIe Switch Downstream Port [1022:43f5] (rev 01) 06:08.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 600 Series Ch= ipset PCIe Switch Downstream Port [1022:43f5] (rev 01) 06:0c.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 600 Series Ch= ipset PCIe Switch Downstream Port [1022:43f5] (rev 01) 06:0d.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] 600 Series Ch= ipset PCIe Switch Downstream Port [1022:43f5] (rev 01) 08:00.0 Ethernet controller [0200]: Intel Corporation Ethernet Controller I= 226-V [8086:125c] (rev 06) 09:00.0 Network controller [0280]: MEDIATEK Corp. MT7925 802.11be 160MHz 2x= 2 PCIe Wireless Network Adapter [Filogic 360] [14c3:7925] 0b:00.0 USB controller [0c03]: Advanced Micro Devices, Inc. [AMD] 800 Serie= s Chipset USB 3.x XHCI Controller [1022:43fc] (rev 01) 0c:00.0 SATA controller [0106]: Advanced Micro Devices, Inc. [AMD] 600 Seri= es Chipset SATA Controller [1022:43f6] (rev 01) 0d:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD= /ATI] Granite Ridge [Radeon Graphics] [1002:13c0] (rev c1) 0d:00.1 Audio device [0403]: Advanced Micro Devices, Inc. [AMD/ATI] Radeon = High Definition Audio Controller [Rembrandt/Strix] [1002:1640] 0d:00.2 Encryption controller [1080]: Advanced Micro Devices, Inc. [AMD] Fa= mily 19h PSP/CCP [1022:1649] 0d:00.3 USB controller [0c03]: Advanced Micro Devices, Inc. [AMD] Raphael/G= ranite Ridge USB 3.1 xHCI [1022:15b6] 0d:00.4 USB controller [0c03]: Advanced Micro Devices, Inc. [AMD] Raphael/G= ranite Ridge USB 3.1 xHCI [1022:15b7] 0e:00.0 USB controller [0c03]: Advanced Micro Devices, Inc. [AMD] Raphael/G= ranite Ridge USB 2.0 xHCI [1022:15b8] Bert Karwatzki