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Mon, 20 Mar 2023 21:25:17 +0100 List-Id: Discussion List-Archive: https://lists.freebsd.org/archives/freebsd-xen List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-xen@freebsd.org X-BeenThere: freebsd-xen@freebsd.org MIME-Version: 1.0 Message-ID: From: Janis Abens To: Xen FreeBSD Subject: Re: Kernel panic due to netback.c Content-Type: text/plain; charset=UTF-8 Date: Mon, 20 Mar 2023 21:25:17 +0100 Importance: normal Sensitivity: Normal Content-Transfer-Encoding: quoted-printable X-Priority: 3 X-Provags-ID: V03:K1:5iVW0tOCEPy0+jlF1kWth/QWCqFUnYz9k7/vZWDyKYfzX/ED0SLFI6N4rNERNmp5FGxVF PX331Ph/dhlSJVd8btZqhAkz4xh0cG/rDjasZir2/cMtYN/i+luBDxlKF/IiVUD3VoXr4UlFlFB8 FlrgjjeuZuFdJFMRx4UrpcbSGFJr/fyuokD+y7Poq3kZwaS5dMnkoA5qCqxf/9myEDYrfsqxXIi4 tXLTd1c1MONS3lL5qOiJS+W22uBIZGz4NUmbz1Ju7w62mvUKFgex4PwDmTxP34p+WS2kIqZwK3+Y CY= X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:GNFlJOr7oSQ=;hHO/lYzhelC/c0DvMnNzb6EDVa+ ic5dZZLCl5MpVTW4dBdD7AeF/Y2B0dcVjLzrB5FVOxZe4m1BaQ7N42CwQjoyJugtPwRiC+OFV MpBlEiwQVdp1eHVSVzDqPPGFp2Hb9+UAn1sQLrxx/BeuDnIS+c/hFKYztIwib9kON4m1sppBW ROiRoGnUqjLVtYoRWfdeB6TOKNCtfTi0xiY2MiOy0ywaBlB1JG84WuMm/tNjMGBs5Ijj3s2fu Bc95HXg5qfxg5E5/Vx4kRRzsL1hw0gwut5qDecAgDpfSFrf1REwPiOG5TkfY/WPPVfqMP0F3M 5k29mSxkRpoS93Vj1RiQ22EBKwhhxaNLibMx9l1THyge5Q37676OLkXJXJ2uDPCcTWjm9ey7V CYySAC7R8D7CZZ1+EpmEfrHucKpSo0ZDuGEQBzHhKP03uWytubrt0M8foSfNJtqf5P3W0wrEZ ZmZvYecLCbVrwOOj0vfCDl1XLYGCrsGBbKLL0uwAPrpRKTW3x2e5JALiyjbD7c3Wyxw4vvIO3 oh5WzGiWS3wtu1oaKSwvG2LN8zvIFwd56nc/rB+06VMDJ+Wk+Cq9HoKOtfe1kcv0EtfJJDpkF V88oxx5NnYrCNhoFH5jrbslFsx3T/lD+2zumu2dQnZjm9vSxJFqJNgMpjygZXy1iZmDV8ucov iO/Fw9RKV60sDbLconVO53l3fvydA637izI6fJ2zUHETN39BWh3VFu4KD0pLgsgmrRYFRpNP4 z1+jp9T4a8cNlZxiAsZBUkOqDf6JCjz2qdrRUGtUVOVHt5WSGRLk5O2dbhtU9d3b4xb5jQbY/ GHNjjnwfaWzf6ZoePKu6R39gr+R6dq9SNcJbgjrunBs/Y= X-Spamd-Result: default: False [-0.44 / 15.00]; FAKE_REPLY(1.00)[]; NEURAL_HAM_MEDIUM(-0.96)[-0.957]; DMARC_POLICY_ALLOW(-0.50)[gmx.com,none]; MID_RHS_NOT_FQDN(0.50)[]; NEURAL_HAM_LONG(-0.29)[-0.286]; NEURAL_SPAM_SHORT(0.20)[0.203]; R_SPF_ALLOW(-0.20)[+ip4:212.227.15.0/24:c]; MIME_GOOD(-0.10)[text/plain]; RCVD_IN_DNSWL_LOW(-0.10)[212.227.15.19:from]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVFROM(0.00)[gmx.com]; MLMMJ_DEST(0.00)[freebsd-xen@FreeBSD.org]; ASN(0.00)[asn:8560, ipnet:212.227.0.0/16, country:DE]; FROM_EQ_ENVFROM(0.00)[]; HAS_X_PRIO_THREE(0.00)[3]; RCVD_TLS_LAST(0.00)[]; RWL_MAILSPIKE_POSSIBLE(0.00)[212.227.15.19:from]; FROM_HAS_DN(0.00)[]; ARC_NA(0.00)[]; TO_DN_ALL(0.00)[]; FREEMAIL_FROM(0.00)[gmx.com]; RCPT_COUNT_ONE(0.00)[1]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2] X-Rspamd-Queue-Id: 4PgR7L6S2qz3Nch X-Spamd-Bar: / X-ThisMailContainsUnwantedMimeParts: N I'm sorry, it's unreadable=2E I sen't it from the new webmail, that has a d= efault setting to HTML=2E Fixing my error and resending previous message as= text=2E =C2=A0 Hello, From time to time a kernel panic occurs=2E Xen-kernel-4=2E15, dom0, FreeBS= D 13=2E0-RELEASE=2E "Fatal trap 12: page fault while in kernel mode" I can not repeat it reliably, but eventually it happens=2E I have captured= a stack trace (always the same on crash), relevant part is: =2E=2E #9 xnb_txpkt2gnttab (pkt=3D, pkt@entry=3D0xfffffe00c49fdac= 8, mbufc=3D, mbufc@entry=3D0xfffff8002f958500, gnttab=3Dgntt= ab@entry=3D0xfffffe019ae94a70, txb=3Dtxb@entry=3D0xfffffe019ae95480, otherend_id=3D6) at /usr/src/sys= /dev/xen/netback/netback=2Ec:1715 #10 0xffffffff80a8d72a in xnb_recv (txb=3D0xfffffe019ae95480, otherend=3D6= , mbufc=3D, ifnet=3D0xfffff80170f81000, gnttab=3D0xfffffe019= ae94a70) at /usr/src/sys/dev/xen/netback/netback=2Ec:1851 #11 xnb_intr (arg=3D0xfffffe019ae94000) at /usr/src/sys/dev/xen/netback/ne= tback=2Ec:1446 =2E=2E It seems netback=2Ec has not changed in ages, same lines are valid in 13= =2E2 RC3 as well=2E relevant code around /usr/src/sys/dev/xen/netback/netback=2Ec:1715 =2E=2E xnb_txpkt2gnttab(const struct xnb_pkt *pkt, struct mbuf *mbufc, =2E=2E while (size_remaining > 0) { const netif_tx_request_t *txq =3D RING_GET_REQUEST(txb, r_idx); const size_t mbuf_space =3D M_TRAILINGSPACE(mbuf) - m_ofs; /* PANIC ha= ppens here! */ =20 =2E=2E By analyzing the trace i've come to conclusion that mbuf is NULL, thus mac= ro: #define M_TRAILINGSPACE(m) ((m)->m_maxlen - (m)->m_len) introduces panic=2E The only way mbuf can become NULL is within this same loop at line:1751 mb= uf =3D mbuf->m_next; It can not be NULL at the function call, because xnb_recv ensures that it = is not NULL, before call=2E The problem definiteley is because while condition is on size_remaining, b= ut contents are accessed based on mbuf->m_next; So my questions are: 1) would it be possible to add some function before the PANIC line (or mbu= f->m_next) that dumps offending packet in error logs or something similar? = The goal for this would be to find a way to reliably repeat this case and u= nderstand what is the cause? If there is no such a function, which variable= s would be relevant and hellpful in this case? 2) How could this code be modified so that it does not panic in this case,= but just drops offending packet instead? A code snippet in xnb_recv has caught my eye: if (*mbufc =3D=3D NULL) { /* * Couldn't allocate mbufs=2E Respond and drop the packet=2E Do * not consume the requests */ xnb_txpkt2rsp(&pkt, txb, 1); DPRINTF("xnb_intr: Couldn't allocate mbufs, num_consumed=3D%d\n", num_consumed); if_inc_counter(ifnet, IFCOUNTER_IQDROPS, 1); return ENOMEM; } Could it be used in function xnb_txpkt2gnttab to avoid panic in this parti= cular case as well? Thank you! Janis Abens =C2=A0