From nobody Sat Jul 12 18:10:03 2025 X-Original-To: current@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 4bfc7R6Z8kz60w4P for ; Sat, 12 Jul 2025 18:10:11 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4bfc7R0xN2z3H0C for ; Sat, 12 Jul 2025 18:10:11 +0000 (UTC) (envelope-from kostikbel@gmail.com) Authentication-Results: mx1.freebsd.org; dkim=none; spf=softfail (mx1.freebsd.org: 2001:470:d5e7:1::1 is neither permitted nor denied by domain of kostikbel@gmail.com) smtp.mailfrom=kostikbel@gmail.com; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=gmail.com (policy=none) Received: from tom.home (kib@localhost [127.0.0.1] (may be forged)) by kib.kiev.ua (8.18.1/8.18.1) with ESMTP id 56CIA48o026432; Sat, 12 Jul 2025 21:10:07 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua 56CIA48o026432 Received: (from kostik@localhost) by tom.home (8.18.1/8.18.1/Submit) id 56CIA3rw026431; Sat, 12 Jul 2025 21:10:03 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Sat, 12 Jul 2025 21:10:03 +0300 From: Konstantin Belousov To: "Bjoern A. Zeeb" Cc: current@freebsd.org Subject: Re: panic: mi_switch: switch in a critical section Message-ID: References: <49s4o954-47r9-1ooq-o536-9o4o95qrqs85@yvfgf.mnoonqbm.arg> List-Id: Discussions about the use of FreeBSD-current List-Archive: https://lists.freebsd.org/archives/freebsd-current List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-current@FreeBSD.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49s4o954-47r9-1ooq-o536-9o4o95qrqs85@yvfgf.mnoonqbm.arg> X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on tom.home X-Spamd-Result: default: False [3.00 / 15.00]; NEURAL_SPAM_MEDIUM(1.00)[1.000]; NEURAL_SPAM_LONG(1.00)[1.000]; NEURAL_SPAM_SHORT(1.00)[0.999]; MIME_GOOD(-0.10)[text/plain]; DMARC_POLICY_SOFTFAIL(0.10)[gmail.com : No valid SPF, No valid DKIM,none]; ARC_NA(0.00)[]; FREEMAIL_FROM(0.00)[gmail.com]; TO_DN_SOME(0.00)[]; ASN(0.00)[asn:6939, ipnet:2001:470::/32, country:US]; RCPT_COUNT_TWO(0.00)[2]; MIME_TRACE(0.00)[0:+]; MISSING_XM_UA(0.00)[]; R_SPF_SOFTFAIL(0.00)[~all]; MLMMJ_DEST(0.00)[current@freebsd.org]; FREEMAIL_ENVFROM(0.00)[gmail.com]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; R_DKIM_NA(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCVD_TLS_LAST(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; HAS_XAW(0.00)[] X-Rspamd-Queue-Id: 4bfc7R0xN2z3H0C X-Spamd-Bar: ++ On Fri, Jul 11, 2025 at 08:56:04AM +0000, Bjoern A. Zeeb wrote: > > # sysctl debug.kdb.enter=1 db> cont > panic: mi_switch: switch in a critical section > cpuid = 3 > time = 1752224052 > KDB: stack backtrace: > db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe007a575d00 > vpanic() at vpanic+0x136/frame 0xfffffe007a575e30 > panic() at panic+0x43/frame 0xfffffe007a575e90 > mi_switch() at mi_switch+0x1b7/frame 0xfffffe007a575eb0 > ast_scheduler() at ast_scheduler+0x45/frame 0xfffffe007a575ed0 > ast_handler() at ast_handler+0xe8/frame 0xfffffe007a575f10 > ast() at ast+0x20/frame 0xfffffe007a575f30 > fast_syscall_common() at fast_syscall_common+0x1a2/frame 0xfffffe007a575f30 > --- syscall (0, FreeBSD ELF64, syscall), rip = 0x9da5012b7aa, rsp = 0x9da4ce76fd8, rbp = 0x9da4ce77020 --- > KDB: enter: panic > [ thread pid 62399 tid 100210 ] > Stopped at kdb_enter+0x33: movq $0,0x103c492(%rip) We manage td->td_critnest with the plain C increments and decrements. This is done both in the top level, and in interrupt handlers (real handlers, not ithreads I mean). In principle, if interrupt handlers always return with the same value of the td_critnest field as entered, it is fine. But if it is not, there is a possibility of loosing updated. I was not able to find a place where such case could occur. Still, out of caution, might be it makes sense to switch to interrupt-safe updates. On x86 it is enough to use INC/DEC instructions, similar to pcb_flags with it OR/AND.