I am following LDD3. I have implemented the read and write functionality for the scull module. whenever I run echo hello > /dev/scull0 to test the write function, I get list_add / list_del corruption and a stack trace.
Here is my code:
#include <linux/module.h>#include <linux/init.h>#include <linux/moduleparam.h>#include <linux/stat.h>#include <linux/types.h>#include <linux/fs.h>#include <linux/cdev.h>#define SCULL_DEV_NO 4MODULE_LICENSE("Dual BSD/GPL");static int scull_major = 0;static int scull_minor = 0;static int scull_nr_devs = 4;static int scull_qset_val = 1000;static int scull_quantum_val = 4000;module_param(scull_major, int, S_IRUGO);static dev_t dev = 0;struct scull_qset{ void **data; struct scull_qset * next;};struct scull_dev{ struct cdev cdev; struct scull_qset *data; int qset; unsigned long size; int quantum; unsigned int access_key; struct semaphore sem;};int scull_trim(struct scull_dev *dev){ struct scull_qset *dptr, *next; int i; int qset = dev->qset; for (dptr = dev->data; dptr; dptr = next){ if (dptr->data){ for(i = 0; i < qset; i++){ kfree(dptr->data[i]); } kfree(dptr->data); dptr->data = NULL; } next = dptr->next; kfree(dptr); } dev->data = NULL; dev->qset = scull_qset_val; dev->size = 0; dev->quantum = scull_quantum_val; return 0;}int scull_open(struct inode * inode, struct file * filp){ struct scull_dev * dev; dev = container_of(inode->i_cdev, struct scull_dev, cdev); filp->private_data = dev; if((filp->f_flags & O_ACCMODE) == O_WRONLY){ scull_trim(dev); } printk(KERN_INFO "scull: Opened device %d\n", iminor(inode)); return 0;}int scull_release(struct inode * inode, struct file * filp){ printk(KERN_INFO "scull: Released device %d\n", iminor(inode)); return 0;}struct scull_qset* scull_follow(struct scull_dev *dev, int item){ struct scull_qset* ptr = dev->data; struct scull_qset* rptr = NULL; for(int i=0; i<item+1; i++){ pr_info("DEBUG: ptr = %p, ptr->next = %p\n", ptr, ptr ? ptr->next : NULL); if(ptr == NULL){ ptr = kmalloc(sizeof(struct scull_qset), GFP_KERNEL); if (ptr == NULL) return NULL; memset(ptr, 0, sizeof(struct scull_qset)); ptr->data = NULL; ptr->next = NULL; } rptr = ptr; ptr = ptr->next; } return rptr;}ssize_t scull_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos){ ssize_t retval = 0; struct scull_dev *dev = filp->private_data; struct scull_qset *dptr; int quantum = dev->quantum, qset = dev->qset; int itemsize = quantum * qset; int item, s_pos, q_pos, rest; if (down_interruptible(&dev->sem)) return -ERESTARTSYS; if (*f_pos >= dev->size) goto out; if (*f_pos + count > dev->size) count = dev->size - *f_pos; item = (long)*f_pos / itemsize; rest = (long)*f_pos % itemsize; s_pos = rest / quantum; q_pos = rest % quantum; dptr = scull_follow(dev, item); if (dptr == NULL || !dptr->data || !dptr->data[s_pos]) goto out; if (count > quantum - q_pos) count = quantum - q_pos; if (copy_to_user(buf, dptr->data[s_pos] + q_pos, count)){ return -EFAULT; goto out; } *f_pos += count; retval = count; out: up(&dev->sem); return retval;}ssize_t scull_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos){ struct scull_dev *dev = filp->private_data; struct scull_qset *dptr; int quantum = dev->quantum, qset = dev->qset; int itemsize = quantum * qset; int item, s_pos, q_pos, rest; ssize_t retval = -ENOMEM; if (down_interruptible(&dev->sem)) return -ERESTARTSYS; item = (long)*f_pos / itemsize; rest = (long)*f_pos % itemsize; s_pos = rest / quantum; q_pos = rest % quantum; dptr = scull_follow(dev, item); if (dptr == NULL) goto out; if (!dptr->data){ dptr->data = kmalloc(sizeof(char *) * dev->qset, GFP_KERNEL); if (!dptr->data) goto out; memset(dptr->data, 0, qset * sizeof(char *)); } if (!dptr->data[s_pos]){ dptr->data[s_pos] = kmalloc(dev->quantum, GFP_KERNEL); if (!dptr->data[s_pos]) goto out; } if (count > quantum - q_pos) count = quantum - q_pos; if (copy_from_user(dptr->data[s_pos] + q_pos, buf, count)){ retval = -EFAULT; goto out; } *f_pos += count; retval = count; if (dev->size < *f_pos) dev->size = *f_pos; out: up(&dev->sem); return retval; }static struct scull_dev scull_devp_array[SCULL_DEV_NO];struct file_operations scull_fops = { .owner = THIS_MODULE, .open = scull_open, .release = scull_release, .read = scull_read, .write = scull_write};static void scull_setup_cdev(struct scull_dev *dev, int index){ dev_t dev_no = MKDEV(scull_major, scull_minor + index); cdev_init(&dev->cdev, &scull_fops); dev->cdev.owner = THIS_MODULE; printk(KERN_INFO "scull: Initialized Major: %d, Minor: %d\n", scull_major, scull_minor + index); int result = cdev_add(&dev->cdev, dev_no, 1); if (result < 0){ printk(KERN_ERR "scull: Failed to add Major: %d, Minor: %d\n", scull_major, scull_minor + index); }}static void scull_rm_cdev(struct scull_dev *dev){ printk(KERN_INFO "scull: Removing cdev\n"); cdev_del(&dev->cdev);}static int __init scull_init(void){ printk(KERN_INFO "scull: Allocating char device...\n"); int result; if(scull_major){ dev = MKDEV(scull_major, scull_minor); result = register_chrdev_region(dev, scull_nr_devs, "scull"); } else{ result = alloc_chrdev_region(&dev, scull_minor, scull_nr_devs, "scull"); scull_major = MAJOR(dev); } if (result < 0){ printk(KERN_WARNING "scull: can't get major %d\n", scull_major); return result; } printk(KERN_INFO "scull: Major is %d", scull_major); for(int i = scull_minor; i < scull_nr_devs; i++){ scull_setup_cdev(&scull_devp_array[i], i); } return 0;}static void __exit scull_exit(void){ printk(KERN_INFO "scull: Exiting...\n"); unregister_chrdev_region(dev, scull_nr_devs); printk(KERN_INFO "scull: Unregistered device\n"); for(int i = scull_minor; i < scull_nr_devs; i++){ scull_rm_cdev(&scull_devp_array[i]); printk(KERN_INFO "scull: Freeing scull_dev %d\n", i); }}module_init(scull_init);module_exit(scull_exit);I ran echo hello > /dev/scull0. The dmesg logs shows list_add corruption. prev is NULL on running the command. When I exit out with Ctrl + C and run the command again, the dmesg logs shows 2 errors, the first being a list_del corruption and the second being a list_add corruption. Here is the dmesg log for the 3 errors:
[43170.630743] scull: Opened device 0[43170.630761] ------------[ cut here ]------------[43170.630764] list_add corruption. prev is NULL.[43170.630773] WARNING: CPU: 6 PID: 57011 at lib/list_debug.c:25 __list_add_valid_or_report+0x42/0xa0[43170.630784] Modules linked in: scull(OE) ntfs3 snd_seq_dummy snd_hrtimer snd_seq ccm nvidia_drm(POE) nvidia_uvm(POE) nvidia_modeset(POE) nvidia(POE) vfat fat intel_rapl_msr intel_rapl_common edac_mce_amd kvm_amd iwlmvm kvm mac80211 irqbypass mousedev snd_usb_audio joydev crct10dif_pclmul crc32_pclmul polyval_clmulni polyval_generic snd_usbmidi_lib snd_ump snd_hda_codec_realtek snd_rawmidi snd_hda_codec_generic snd_seq_device ledtrig_audio gf128mul snd_hda_codec_hdmi mc ghash_clmulni_intel sha512_ssse3 sha256_ssse3 sha1_ssse3 aesni_intel snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec libarc4 snd_hda_core btusb btrtl btintel iwlwifi btbcm snd_hwdep btmtk snd_pcm bluetooth cfg80211 snd_timer snd r8169 crypto_simd cryptd ecdh_generic rapl soundcore realtek sp5100_tco mdio_devres k10temp libphy rfkill i2c_piix4 video ccp gigabyte_wmi wmi_bmof pcspkr acpi_cpufreq gpio_amdpt wmi mac_hid gpio_generic i2c_dev crypto_user loop fuse dm_mod nfnetlink ip_tables x_tables ext4 crc32c_generic crc16 mbcache jbd2[43170.630928] usbhid nvme nvme_core crc32c_intel xhci_pci xhci_pci_renesas nvme_auth[43170.630941] Unloaded tainted modules: scull(OE):13 [last unloaded: scull(OE)][43170.630951] CPU: 6 PID: 57011 Comm: bash Tainted: P R D W OE 6.7.0-arch3-1 #1 29ada86f174bb9983ea57568622d66509982ed7e[43170.630957] Hardware name: Gigabyte Technology Co., Ltd. B450M DS3H WIFI/B450M DS3H WIFI-CF, BIOS F52 01/07/2021[43170.630960] RIP: 0010:__list_add_valid_or_report+0x42/0xa0[43170.630966] Code: 75 41 4c 8b 02 49 39 c0 75 4c 48 39 fa 74 60 49 39 f8 74 5b b8 01 00 00 00 e9 fa 05 77 00 48 c7 c7 d0 c7 2a 92 e8 fe 24 a5 ff <0f> 0b 31 c0 e9 e5 05 77 00 48 c7 c7 f8 c7 2a 92 e8 e9 24 a5 ff 0f[43170.630970] RSP: 0018:ffffad82c1e9bcf8 EFLAGS: 00010082[43170.630975] RAX: 0000000000000000 RBX: 7fffffffffffffff RCX: 0000000000000027[43170.630979] RDX: ffff89f40e9a16c8 RSI: 0000000000000001 RDI: ffff89f40e9a16c0[43170.630982] RBP: ffffad82c1e9bd68 R08: 0000000000000000 R09: ffffad82c1e9bb80[43170.630985] R10: 0000000000000003 R11: ffff89f41f32b368 R12: ffffffffc24b87c8[43170.630989] R13: 0000000000000001 R14: 0000000000000000 R15: ffffffffc24b87d0[43170.630992] FS: 00007747f80d6740(0000) GS:ffff89f40e980000(0000) knlGS:0000000000000000[43170.630997] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033[43170.631000] CR2: 0000563ef7be1000 CR3: 00000001c487c000 CR4: 0000000000350ef0[43170.631004] Call Trace:[43170.631008] <TASK>[43170.631011] ? __list_add_valid_or_report+0x42/0xa0[43170.631016] ? __warn+0x81/0x130[43170.631025] ? __list_add_valid_or_report+0x42/0xa0[43170.631030] ? report_bug+0x171/0x1a0[43170.631037] ? prb_read_valid+0x1b/0x30[43170.631043] ? srso_return_thunk+0x5/0x5f[43170.631050] ? handle_bug+0x3c/0x80[43170.631057] ? exc_invalid_op+0x17/0x70[43170.631063] ? asm_exc_invalid_op+0x1a/0x20[43170.631074] ? __list_add_valid_or_report+0x42/0xa0[43170.631080] ? __list_add_valid_or_report+0x42/0xa0[43170.631084] __down_common+0x71/0x230[43170.631095] down_interruptible+0x52/0x60[43170.631101] scull_write+0x4c/0x200 [scull bd55e810425245067618b333771c8e3ae1dc9535][43170.631114] vfs_write+0xf2/0x400[43170.631127] ksys_write+0x6f/0xf0[43170.631135] do_syscall_64+0x64/0xe0[43170.631140] ? srso_return_thunk+0x5/0x5f[43170.631145] ? syscall_exit_to_user_mode+0x2b/0x40[43170.631150] ? srso_return_thunk+0x5/0x5f[43170.631155] ? do_syscall_64+0x70/0xe0[43170.631159] ? srso_return_thunk+0x5/0x5f[43170.631164] ? do_syscall_64+0x70/0xe0[43170.631169] ? srso_return_thunk+0x5/0x5f[43170.631174] ? exc_page_fault+0x7f/0x180[43170.631180] entry_SYSCALL_64_after_hwframe+0x6e/0x76[43170.631186] RIP: 0033:0x7747f8254034[43170.631209] Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d 35 c3 0d 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 48 83 ec 28 48 89 54 24 18 48[43170.631213] RSP: 002b:00007fffe0667af8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001[43170.631218] RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007747f8254034[43170.631222] RDX: 0000000000000006 RSI: 0000563ef7bde970 RDI: 0000000000000001[43170.631225] RBP: 0000563ef7bde970 R08: 0000000000000073 R09: 0000000000000001[43170.631228] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000006[43170.631232] R13: 00007747f83295c0 R14: 00007747f8326f20 R15: 0000000000000000[43170.631241] </TASK>[43170.631244] ---[ end trace 0000000000000000 ]---[43188.138981] ------------[ cut here ]------------[43188.138987] list_del corruption, ffffad82c1e9bd10->next is NULL[43188.138999] WARNING: CPU: 6 PID: 57011 at lib/list_debug.c:52 __list_del_entry_valid_or_report+0x5d/0xe0[43188.139009] Modules linked in: scull(OE) ntfs3 snd_seq_dummy snd_hrtimer snd_seq ccm nvidia_drm(POE) nvidia_uvm(POE) nvidia_modeset(POE) nvidia(POE) vfat fat intel_rapl_msr intel_rapl_common edac_mce_amd kvm_amd iwlmvm kvm mac80211 irqbypass mousedev snd_usb_audio joydev crct10dif_pclmul crc32_pclmul polyval_clmulni polyval_generic snd_usbmidi_lib snd_ump snd_hda_codec_realtek snd_rawmidi snd_hda_codec_generic snd_seq_device ledtrig_audio gf128mul snd_hda_codec_hdmi mc ghash_clmulni_intel sha512_ssse3 sha256_ssse3 sha1_ssse3 aesni_intel snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec libarc4 snd_hda_core btusb btrtl btintel iwlwifi btbcm snd_hwdep btmtk snd_pcm bluetooth cfg80211 snd_timer snd r8169 crypto_simd cryptd ecdh_generic rapl soundcore realtek sp5100_tco mdio_devres k10temp libphy rfkill i2c_piix4 video ccp gigabyte_wmi wmi_bmof pcspkr acpi_cpufreq gpio_amdpt wmi mac_hid gpio_generic i2c_dev crypto_user loop fuse dm_mod nfnetlink ip_tables x_tables ext4 crc32c_generic crc16 mbcache jbd2[43188.139153] usbhid nvme nvme_core crc32c_intel xhci_pci xhci_pci_renesas nvme_auth[43188.139166] Unloaded tainted modules: scull(OE):13 [last unloaded: scull(OE)][43188.139175] CPU: 6 PID: 57011 Comm: bash Tainted: P R D W OE 6.7.0-arch3-1 #1 29ada86f174bb9983ea57568622d66509982ed7e[43188.139182] Hardware name: Gigabyte Technology Co., Ltd. B450M DS3H WIFI/B450M DS3H WIFI-CF, BIOS F52 01/07/2021[43188.139186] RIP: 0010:__list_del_entry_valid_or_report+0x5d/0xe0[43188.139191] Code: 48 8b 01 48 39 f8 75 67 48 8b 72 08 48 39 c6 75 74 b8 01 00 00 00 e9 32 05 77 00 48 89 fe 48 c7 c7 f8 c8 2a 92 e8 33 24 a5 ff <0f> 0b 31 c0 e9 1a 05 77 00 48 89 fe 48 c7 c7 20 c9 2a 92 e8 1b 24[43188.139196] RSP: 0018:ffffad82c1e9bcf8 EFLAGS: 00010082[43188.139200] RAX: 0000000000000000 RBX: 7fffffffffffffff RCX: 0000000000000027[43188.139204] RDX: ffff89f40e9a16c8 RSI: 0000000000000001 RDI: ffff89f40e9a16c0[43188.139208] RBP: ffffad82c1e9bd68 R08: 0000000000000000 R09: ffffad82c1e9bb80[43188.139211] R10: 0000000000000003 R11: ffff89f41f32b368 R12: ffffffffc24b87c8[43188.139214] R13: 0000000000000001 R14: 0000000000000001 R15: ffff89f270b10000[43188.139217] FS: 00007747f80d6740(0000) GS:ffff89f40e980000(0000) knlGS:0000000000000000[43188.139222] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033[43188.139225] CR2: 00007740023bd698 CR3: 00000001c487c000 CR4: 0000000000350ef0[43188.139229] Call Trace:[43188.139233] <TASK>[43188.139236] ? __list_del_entry_valid_or_report+0x5d/0xe0[43188.139241] ? __warn+0x81/0x130[43188.139248] ? __list_del_entry_valid_or_report+0x5d/0xe0[43188.139253] ? report_bug+0x171/0x1a0[43188.139261] ? prb_read_valid+0x1b/0x30[43188.139267] ? srso_return_thunk+0x5/0x5f[43188.139274] ? handle_bug+0x3c/0x80[43188.139280] ? exc_invalid_op+0x17/0x70[43188.139286] ? asm_exc_invalid_op+0x1a/0x20[43188.139298] ? __list_del_entry_valid_or_report+0x5d/0xe0[43188.139304] ? __list_del_entry_valid_or_report+0x5d/0xe0[43188.139308] __down_common+0xdb/0x230[43188.139318] down_interruptible+0x52/0x60[43188.139325] scull_write+0x4c/0x200 [scull bd55e810425245067618b333771c8e3ae1dc9535][43188.139338] vfs_write+0xf2/0x400[43188.139350] ksys_write+0x6f/0xf0[43188.139358] do_syscall_64+0x64/0xe0[43188.139363] ? srso_return_thunk+0x5/0x5f[43188.139368] ? syscall_exit_to_user_mode+0x2b/0x40[43188.139373] ? srso_return_thunk+0x5/0x5f[43188.139378] ? do_syscall_64+0x70/0xe0[43188.139382] ? srso_return_thunk+0x5/0x5f[43188.139387] ? do_syscall_64+0x70/0xe0[43188.139392] ? srso_return_thunk+0x5/0x5f[43188.139397] ? exc_page_fault+0x7f/0x180[43188.139403] entry_SYSCALL_64_after_hwframe+0x6e/0x76[43188.139409] RIP: 0033:0x7747f8254034[43188.139432] Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d 35 c3 0d 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 48 83 ec 28 48 89 54 24 18 48[43188.139436] RSP: 002b:00007fffe0667af8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001[43188.139442] RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007747f8254034[43188.139445] RDX: 0000000000000006 RSI: 0000563ef7bde970 RDI: 0000000000000001[43188.139448] RBP: 0000563ef7bde970 R08: 0000000000000073 R09: 0000000000000001[43188.139452] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000006[43188.139455] R13: 00007747f83295c0 R14: 00007747f8326f20 R15: 0000000000000000[43188.139464] </TASK>[43188.139467] ---[ end trace 0000000000000000 ]---[43188.139503] scull: Released device 0[43189.594736] scull: Opened device 0[43189.594753] ------------[ cut here ]------------[43189.594757] list_add corruption. prev is NULL.[43189.594766] WARNING: CPU: 6 PID: 57011 at lib/list_debug.c:25 __list_add_valid_or_report+0x42/0xa0[43189.594777] Modules linked in: scull(OE) ntfs3 snd_seq_dummy snd_hrtimer snd_seq ccm nvidia_drm(POE) nvidia_uvm(POE) nvidia_modeset(POE) nvidia(POE) vfat fat intel_rapl_msr intel_rapl_common edac_mce_amd kvm_amd iwlmvm kvm mac80211 irqbypass mousedev snd_usb_audio joydev crct10dif_pclmul crc32_pclmul polyval_clmulni polyval_generic snd_usbmidi_lib snd_ump snd_hda_codec_realtek snd_rawmidi snd_hda_codec_generic snd_seq_device ledtrig_audio gf128mul snd_hda_codec_hdmi mc ghash_clmulni_intel sha512_ssse3 sha256_ssse3 sha1_ssse3 aesni_intel snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec libarc4 snd_hda_core btusb btrtl btintel iwlwifi btbcm snd_hwdep btmtk snd_pcm bluetooth cfg80211 snd_timer snd r8169 crypto_simd cryptd ecdh_generic rapl soundcore realtek sp5100_tco mdio_devres k10temp libphy rfkill i2c_piix4 video ccp gigabyte_wmi wmi_bmof pcspkr acpi_cpufreq gpio_amdpt wmi mac_hid gpio_generic i2c_dev crypto_user loop fuse dm_mod nfnetlink ip_tables x_tables ext4 crc32c_generic crc16 mbcache jbd2[43189.594923] usbhid nvme nvme_core crc32c_intel xhci_pci xhci_pci_renesas nvme_auth[43189.594936] Unloaded tainted modules: scull(OE):13 [last unloaded: scull(OE)][43189.594945] CPU: 6 PID: 57011 Comm: bash Tainted: P R D W OE 6.7.0-arch3-1 #1 29ada86f174bb9983ea57568622d66509982ed7e[43189.594951] Hardware name: Gigabyte Technology Co., Ltd. B450M DS3H WIFI/B450M DS3H WIFI-CF, BIOS F52 01/07/2021[43189.594955] RIP: 0010:__list_add_valid_or_report+0x42/0xa0[43189.594960] Code: 75 41 4c 8b 02 49 39 c0 75 4c 48 39 fa 74 60 49 39 f8 74 5b b8 01 00 00 00 e9 fa 05 77 00 48 c7 c7 d0 c7 2a 92 e8 fe 24 a5 ff <0f> 0b 31 c0 e9 e5 05 77 00 48 c7 c7 f8 c7 2a 92 e8 e9 24 a5 ff 0f[43189.594964] RSP: 0018:ffffad82c1e9bd28 EFLAGS: 00010086[43189.594970] RAX: 0000000000000000 RBX: 7fffffffffffffff RCX: 0000000000000027[43189.594973] RDX: ffff89f40e9a16c8 RSI: 0000000000000001 RDI: ffff89f40e9a16c0[43189.594977] RBP: ffffad82c1e9bd98 R08: 0000000000000000 R09: ffffad82c1e9bbb0[43189.594980] R10: 0000000000000003 R11: ffff89f41f32b368 R12: ffffffffc24b87c8[43189.594983] R13: 0000000000000001 R14: 0000000000000000 R15: ffffffffc24b87d0[43189.594987] FS: 00007747f80d6740(0000) GS:ffff89f40e980000(0000) knlGS:0000000000000000[43189.594991] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033[43189.594995] CR2: 00007740023bd698 CR3: 00000001c487c000 CR4: 0000000000350ef0[43189.594999] Call Trace:[43189.595003] <TASK>[43189.595006] ? __list_add_valid_or_report+0x42/0xa0[43189.595011] ? __warn+0x81/0x130[43189.595020] ? __list_add_valid_or_report+0x42/0xa0[43189.595026] ? report_bug+0x171/0x1a0[43189.595033] ? prb_read_valid+0x1b/0x30[43189.595038] ? srso_return_thunk+0x5/0x5f[43189.595046] ? handle_bug+0x3c/0x80[43189.595052] ? exc_invalid_op+0x17/0x70[43189.595058] ? asm_exc_invalid_op+0x1a/0x20[43189.595069] ? __list_add_valid_or_report+0x42/0xa0[43189.595075] ? __list_add_valid_or_report+0x42/0xa0[43189.595079] __down_common+0x71/0x230[43189.595090] down_interruptible+0x52/0x60[43189.595096] scull_write+0x4c/0x200 [scull bd55e810425245067618b333771c8e3ae1dc9535][43189.595109] vfs_write+0xf2/0x400[43189.595117] ? srso_return_thunk+0x5/0x5f[43189.595122] ? syscall_exit_to_user_mode+0x2b/0x40[43189.595127] ? srso_return_thunk+0x5/0x5f[43189.595131] ? do_syscall_64+0x70/0xe0[43189.595136] ? srso_return_thunk+0x5/0x5f[43189.595141] ? filp_flush+0x52/0x80[43189.595149] ksys_write+0x6f/0xf0[43189.595157] do_syscall_64+0x64/0xe0[43189.595162] ? do_syscall_64+0x70/0xe0[43189.595166] ? syscall_exit_to_user_mode+0x2b/0x40[43189.595171] ? srso_return_thunk+0x5/0x5f[43189.595175] ? do_syscall_64+0x70/0xe0[43189.595180] ? srso_return_thunk+0x5/0x5f[43189.595184] ? syscall_exit_to_user_mode+0x2b/0x40[43189.595189] ? srso_return_thunk+0x5/0x5f[43189.595194] ? do_syscall_64+0x70/0xe0[43189.595199] entry_SYSCALL_64_after_hwframe+0x6e/0x76[43189.595205] RIP: 0033:0x7747f8254034[43189.595228] Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d 35 c3 0d 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 48 83 ec 28 48 89 54 24 18 48[43189.595232] RSP: 002b:00007fffe0667af8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001[43189.595237] RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007747f8254034[43189.595241] RDX: 0000000000000006 RSI: 0000563ef7bde970 RDI: 0000000000000001[43189.595244] RBP: 0000563ef7bde970 R08: 0000000000000073 R09: 0000000000000001[43189.595247] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000006[43189.595250] R13: 00007747f83295c0 R14: 00007747f8326f20 R15: 0000000000000000[43189.595260] </TASK>[43189.595263] ---[ end trace 0000000000000000 ]---I tested to see if it was an issue with the scull_follow function by removing everything in the write function and just using down_interruptible and printk to see if that was the case. I was encountering the same issue. I am hypothesising that the issue has something to do with the semaphore. Please guide me on what to do.