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Thu, 29 Jul 2021 02:48:43 -0700 (PDT) Date: Thu, 29 Jul 2021 18:48:35 +0900 From: William Breathitt Gray To: jic23@kernel.org Cc: linux-stm32@st-md-mailman.stormreply.com, kernel@pengutronix.de, a.fatoum@pengutronix.de, kamel.bouhara@bootlin.com, gwendal@chromium.org, alexandre.belloni@bootlin.com, david@lechnology.com, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com, patrick.havelange@essensium.com, fabrice.gasnier@st.com, mcoquelin.stm32@gmail.com, alexandre.torgue@st.com, o.rempel@pengutronix.de, jarkko.nikula@linux.intel.com Subject: Re: [PATCH v13 00/17] Introduce the Counter character device interface Message-ID: References: MIME-Version: 1.0 In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210729_024848_417883_80524968 X-CRM114-Status: GOOD ( 31.01 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: multipart/mixed; boundary="===============8346198989092128064==" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org --===============8346198989092128064== Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="TqnZt1+pCWg0OOJI" Content-Disposition: inline --TqnZt1+pCWg0OOJI Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Jul 28, 2021 at 05:51:45PM +0900, William Breathitt Gray wrote: > On Tue, Jul 13, 2021 at 06:53:04PM +0900, William Breathitt Gray wrote: > > Suppose I open the chrdev from a userspace application and keep it open, > > but then remove the respective driver and Counter subsystem module from > > my system. The devm_counter_release() and counter_exit() functions will > > be called as expected; the counter_chrdev_release() function will not be > > called yet, but that is expected because the chrdev is still open by > > userspace. If I try to break out of my userspace application, I expect > > counter_chrdev_release() to finally be called, but this does not happen. > > Instead, my userspace application stalls and I see the following error > > in my dmesg: > >=20 > > [ 172.859570] BUG: unable to handle page fault for address: ffffffffc0= 9ae298 > > [ 172.859594] #PF: supervisor read access in kernel mode > > [ 172.859598] #PF: error_code(0x0000) - not-present page > > [ 172.859603] PGD 23615067 P4D 23615067 PUD 23617067 PMD 1029ad067 PTE= 0 > > [ 172.859623] Oops: 0000 [#1] SMP NOPTI > > [ 172.859629] CPU: 2 PID: 2485 Comm: counter_example Not tainted 5.13.= 0+ #1 > > [ 172.859640] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), B= IOS d55cb5a 04/01/2014 > > [ 172.859645] RIP: 0010:filp_close+0x29/0x70 > > [ 172.859662] Code: 90 0f 1f 44 00 00 55 48 89 e5 41 56 41 55 41 54 48= 8b 47 38 48 85 c0 0f 84 b7 40 86 00 48 8b 47 28 49 89 fc 49 89 f5 45 31 f6= <48> 8b 40 78 48 85 c0 74 08 ff d0 0f 1f 00 41 89 c6 41 f6 44 24 45 > > [ 172.859669] RSP: 0018:ffffad31c0ee7cb0 EFLAGS: 00010246 > > [ 172.859675] RAX: ffffffffc09ae220 RBX: 0000000000000001 RCX: 0000000= 000000001 > > [ 172.859680] RDX: ffff9a43829708e0 RSI: ffff9a4382970840 RDI: ffff9a4= 3821f4f00 > > [ 172.859684] RBP: ffffad31c0ee7cc8 R08: 0000000000000001 R09: 0000000= 000000001 > > [ 172.859687] R10: ffffffffffff4d00 R11: ffff9a43933c6e10 R12: ffff9a4= 3821f4f00 > > [ 172.859691] R13: ffff9a4382970840 R14: 0000000000000000 R15: 0000000= 000000003 > > [ 172.859694] FS: 0000000000000000(0000) GS:ffff9a44b7d00000(0000) kn= lGS:0000000000000000 > > [ 172.859699] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [ 172.859704] CR2: ffffffffc09ae298 CR3: 0000000023610001 CR4: 0000000= 000370ee0 > > [ 172.859713] Call Trace: > > [ 172.859730] put_files_struct+0x73/0xd0 > > [ 172.859738] exit_files+0x49/0x50 > > [ 172.859743] do_exit+0x33b/0xa20 > > [ 172.859751] do_group_exit+0x3b/0xb0 > > [ 172.859758] get_signal+0x16f/0x8b0 > > [ 172.859766] ? _copy_to_user+0x20/0x30 > > [ 172.859774] ? put_timespec64+0x3d/0x60 > > [ 172.859784] arch_do_signal_or_restart+0xf3/0x850 > > [ 172.859794] ? hrtimer_nanosleep+0x9f/0x120 > > [ 172.859802] ? __hrtimer_init+0xd0/0xd0 > > [ 172.859808] exit_to_user_mode_prepare+0x122/0x1b0 > > [ 172.859816] syscall_exit_to_user_mode+0x27/0x50 > > [ 172.859825] do_syscall_64+0x48/0xc0 > > [ 172.859831] entry_SYSCALL_64_after_hwframe+0x44/0xae > > [ 172.859839] RIP: 0033:0x7f07f8b9951a > > [ 172.859850] Code: Unable to access opcode bytes at RIP 0x7f07f8b994f= 0. > > [ 172.859853] RSP: 002b:00007ffc0d12c230 EFLAGS: 00000246 ORIG_RAX: 00= 000000000000e6 > > [ 172.859860] RAX: fffffffffffffdfc RBX: ffffffffffffff01 RCX: 00007f0= 7f8b9951a > > [ 172.859863] RDX: 00007ffc0d12c2b0 RSI: 0000000000000000 RDI: 0000000= 000000000 > > [ 172.859867] RBP: 0000000000000000 R08: 0000000000000000 R09: 00007ff= c0d12c1c6 > > [ 172.859871] R10: 00007ffc0d12c2b0 R11: 0000000000000246 R12: 00007ff= c0d12c2b0 > > [ 172.859874] R13: 00007ffc0d12c2b0 R14: 0000000000000000 R15: 0000000= 000000000 > > [ 172.859886] Modules linked in: intel_rapl_msr intel_rapl_common kvm_= intel kvm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel nls_iso8859_1 a= esni_intel crypto_simd cryptd rapl drm_ttm_helper ttm uvcvideo drm_kms_help= er videobuf2_vmalloc videobuf2_memops videobuf2_v4l2 videobuf2_common input= _leds syscopyarea videodev sysfillrect sysimgblt fb_sys_fops cec rc_core jo= ydev mc drm serio_raw mac_hid qemu_fw_cfg sch_fq_codel msr parport_pc ppdev= lp parport virtio_rng ip_tables x_tables autofs4 hid_generic usbhid hid vi= rtio_net psmouse net_failover i2c_piix4 virtio_blk failover pata_acpi flopp= y [last unloaded: counter] > > [ 172.859995] CR2: ffffffffc09ae298 > > [ 172.860009] ---[ end trace e7d3d7da1a73b8f4 ]--- > > [ 172.860013] RIP: 0010:filp_close+0x29/0x70 > > [ 172.860021] Code: 90 0f 1f 44 00 00 55 48 89 e5 41 56 41 55 41 54 48= 8b 47 38 48 85 c0 0f 84 b7 40 86 00 48 8b 47 28 49 89 fc 49 89 f5 45 31 f6= <48> 8b 40 78 48 85 c0 74 08 ff d0 0f 1f 00 41 89 c6 41 f6 44 24 45 > > [ 172.860027] RSP: 0018:ffffad31c0ee7cb0 EFLAGS: 00010246 > > [ 172.860031] RAX: ffffffffc09ae220 RBX: 0000000000000001 RCX: 0000000= 000000001 > > [ 172.860034] RDX: ffff9a43829708e0 RSI: ffff9a4382970840 RDI: ffff9a4= 3821f4f00 > > [ 172.860038] RBP: ffffad31c0ee7cc8 R08: 0000000000000001 R09: 0000000= 000000001 > > [ 172.860041] R10: ffffffffffff4d00 R11: ffff9a43933c6e10 R12: ffff9a4= 3821f4f00 > > [ 172.860044] R13: ffff9a4382970840 R14: 0000000000000000 R15: 0000000= 000000003 > > [ 172.860047] FS: 0000000000000000(0000) GS:ffff9a44b7d00000(0000) kn= lGS:0000000000000000 > > [ 172.860052] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [ 172.860056] CR2: ffffffffc09ae298 CR3: 0000000023610001 CR4: 0000000= 000370ee0 > > [ 172.860073] Fixing recursive fault but reboot is needed! > >=20 > > It looks like faults in filp_close() before counter_chrdev_release() is > > called. Is this issue manifesting because counter_exit() was called > > earlier while the chrdev was still open? >=20 > After giving this some more thought I realized that once the counter > module is unloaded, the counter_fops callbacks are lost and thus the > fops for the chrdev are no longer be valid. This means that > counter_chrdev_release will need to be called before the counter module > is unloaded. How can I guarantee this if a userspace application may > still have the chrdev indefinitely open? In counter_chrdev_remove(), > should I walk through the open chrdevs and release each one? >=20 > William Breathitt Gray Sorry for all the noise, I had simply forgotten to define the owner member of counter_fops structure to THIS_MODULE. I'll make that fix and also add in some conditional checks to protect the callbacks so they return -ENODEV if the counter has been unregistered. With that I expect to have a v14 submission ready some time this coming week. William Breathitt Gray --TqnZt1+pCWg0OOJI Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEk5I4PDJ2w1cDf/bghvpINdm7VJIFAmECeWkACgkQhvpINdm7 VJLWPw/9Gvy1Am3dCnOtIeE+VRrEZ+PD6w4p3uhoBgBNRSDbHOM3TAAYynG1myLB CgV1I8EwG9TEMWXp2EoxjrQr8HgsblGjBwm+qnKO4MAEldms2HEHknaZL2h9/T2/ TIIXC6Be5egf3zH9dZ2BmbtSN1A6qlJ1384CThpO8XE3aINjL8ye4N5TjQp3UuPT sRrkQJnzsQ7lX1IuLmIgLqd8/SGC5+QBYSTLLIUmxQd5UBXEEqKsSM2FzUmRc6XN SjTWgWOKcGcrN87gz/ZnCexTXN6QZ0Hv27N6EiHN0CsOlRCib01PiVXhNneGw8uL 0jG0zyOLE5RLDv0gpwh+qz2JuZGSPenZjHnxp6ipWM4gMuCs0da1+4gR4UFA98m9 HH7L5qJy2vA7thqcfAqbxtAWX+NvG225cZlmcqBYrYGhJZXoxjZgfiw5NrA0onLN Q2XBsDr6Oix6CfKpP6YLphbHaZjV++HoCrX83helg6Kry89yJMRMfjPmxUbZYdJC g9EhcihevOUjs+ftvkAaVI2fkhKPOyA8WGmU3/Ft3XI9PA82dKxeUSsZrWIM3Q8w PlJE87GMBWgXx6oO9+2N9epIlMhvBNXa6TY382Q8zrbrGWJfp9S6PD0BZUx3boJl rU7B2AktQWrJFenBZ/Ryy0RSzzDrjnQ9T2cwvtEA2TFYb0LGlzw= =PKVq -----END PGP SIGNATURE----- --TqnZt1+pCWg0OOJI-- --===============8346198989092128064== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel --===============8346198989092128064==--