title: what are differences between kmalloc() kcalloc() vmalloc() and kzalloc()?
body: <pre><code>Hi all, 
  </code></pre>
  
  <p>I'm currently debugging a device driver and I'm getting a kernel panic. After checking the backtrace or the error log, it appears to be that the problem is with kmalloc. I was thinking maybe I could change kmalloc with other allocation functions. What are their differences? </p>
  
  <p>here's the error log: </p>
  
  <pre><code>Unable to handle kernel NULL pointer dereference at virtual address 0000000d
  pgd = c7bdc000
  [0000000d] *pgd=4785f031, *pte=00000000, *ppte=00000000
  Internal error: Oops: 17 [#1] PREEMPT
  Modules linked in: bcm5892_secdom_fw(P) bcm5892_lcd snd_bcm5892 msr bcm5892_sci     bcm589x_ohci_p12 bcm5892_skeypad hx_decoder(P) pinnacle hx_memalloc(P) bcm_udc_dwc         scsi_mod g_serial sd_mod usb_storage
  CPU: 0    Tainted: P           (2.6.27.39-WR3.0.2ax_standard #1)
  PC is at __kmalloc+0x70/0xdc
  LR is at __kmalloc+0x48/0xdc
  pc : [&lt;c0098cc8&gt;]    lr : [&lt;c0098ca0&gt;]    psr: 20000093
  sp : c7a9fd50  ip : c03a4378  fp : c7a9fd7c
  r10: bf0708b4  r9 : c7a9e000  r8 : 00000040
  r7 : bf06d03c  r6 : 00000020  r5 : a0000093  r4 : 0000000d
  r3 : 00000000  r2 : 00000094  r1 : 00000020  r0 : c03a4378
  Flags: nzCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment user
  Control: 00c5387d  Table: 47bdc008  DAC: 00000015
  Process sh (pid: 1088, stack limit = 0xc7a9e260)
  Stack: (0xc7a9fd50 to 0xc7aa0000)
  fd40:                                     c7a6a1d0 00000020 c7a9fd7c c7ba8fc0
  fd60: 00000040 c7a6a1d0 00000020 c71598c0 c7a9fd9c c7a9fd80 bf06d03c c0098c64
  fd80: c71598c0 00000003 c7a6a1d0 bf06c83c c7a9fdbc c7a9fda0 bf06d098 bf06d008
  fda0: c7159880 00000000 c7a6a2d8 c7159898 c7a9fde4 c7a9fdc0 bf06d130 bf06d078
  fdc0: c79ca000 c7159880 00000000 00000000 c7afbc00 c7a9e000 c7a9fe0c c7a9fde8
  fde0: bf06d4b4 bf06d0f0 00000000 c79fd280 00000000 0f700000 c7a9e000 00000241
  fe00: c7a9fe3c c7a9fe10 c01c37b4 bf06d300 00000000 c7afbc00 00000000 00000000
  fe20: c79cba84 c7463c78 c79fd280 c7473b00 c7a9fe6c c7a9fe40 c00a184c c01c35e4
  fe40: 00000000 c7bb0005 c7a9fe64 c79fd280 c7463c78 00000000 c00a1640 c785e380
  fe60: c7a9fe94 c7a9fe70 c009c438 c00a164c c79fd280 c7a9fed8 c7a9fed8 00000003
  fe80: 00000242 00000000 c7a9feb4 c7a9fe98 c009c614 c009c2a4 00000000 c7a9fed8
  fea0: c7a9fed8 00000000 c7a9ff64 c7a9feb8 c00aa6bc c009c5e8 00000242 000001b6
  fec0: 000001b6 00000241 00000022 00000000 00000000 c7a9fee0 c785e380 c7473b00
  fee0: d8666b0d 00000006 c7bb0005 00000300 00000000 00000000 00000001 40002000
  ff00: c7a9ff70 c79b10a0 c79b10a0 00005402 00000003 c78d69c0 ffffff9c 00000242
  ff20: 000001b6 c79fd280 c7a9ff64 c7a9ff38 c785e380 c7473b00 00000000 00000241
  ff40: 000001b6 ffffff9c 00000003 c7bb0000 c7a9e000 00000000 c7a9ff94 c7a9ff68
  ff60: c009c128 c00aa380 4d18b5f0 08000000 00000000 00071214 0007128c 00071214
  ff80: 00000005 c0027ee4 c7a9ffa4 c7a9ff98 c009c274 c009c0d8 00000000 c7a9ffa8
  ffa0: c0027d40 c009c25c 00071214 0007128c 0007128c 00000241 000001b6 00000000
  ffc0: 00071214 0007128c 00071214 00000005 00073580 00000003 000713e0 400010d0
  ffe0: 00000001 bef0c7b8 000269cc 4d214fec 60000010 0007128c 00000000 00000000
  
  
  Backtrace:
  
  [&lt;c0098c58&gt;] (__kmalloc+0x0/0xdc) from [&lt;bf010a00&gt;] (GadgetEpRequestAlloc+0x28/0x70 [bcm_udc_dwc])
  
   r8:bf017c80 r7:c79de2d8 r6:c79de2d8 r5:00000000 r4:00000040
  
  [&lt;bf0109d8&gt;] (GadgetEpRequestAlloc+0x0/0x70 [bcm_udc_dwc]) from [&lt;bf0181d4&gt;] (gs_alloc_req+0x44/0xf0 [g_serial])
  
   r5:00000000 r4:00000040
  
  [&lt;bf018190&gt;] (gs_alloc_req+0x0/0xf0 [g_serial]) from [&lt;bf0182b4&gt;]     (gs_alloc_requests+0x34/0xb4 [g_serial])
  
   r7:c79de2d8 r6:c79aa198 r5:00000000 r4:c79aa180
  
  [&lt;bf018280&gt;] (gs_alloc_requests+0x0/0xb4 [g_serial]) from [&lt;bf018368&gt;] (gs_start_io+0x34/0xb8 [g_serial])
  
   r9:c7b84000 r8:c7b48c00 r7:c79aa198 r6:c79de2d8 r5:c79aa180
  r4:c79aa180
  
  [&lt;bf018334&gt;] (gs_start_io+0x0/0xb8 [g_serial]) from [&lt;bf018730&gt;] (gs_open+0x1d0/0x23c [g_serial])
  
   r9:c7b84000 r8:c7b48c00 r7:00000000 r6:00000000 r5:c79aa180
  r4:c7924300
  
  [&lt;bf018560&gt;] (gs_open+0x0/0x23c [g_serial]) from [&lt;c01c3754&gt;] (tty_open+0x1dc/0x314)
  
  [&lt;c01c3578&gt;] (tty_open+0x0/0x314) from [&lt;c00a184c&gt;] (chrdev_open+0x20c/0x22c)
  
  [&lt;c00a1640&gt;] (chrdev_open+0x0/0x22c) from [&lt;c009c438&gt;] (__dentry_open+0x1a0/0x2b8)
  
   r8:c79aa300 r7:c00a1640 r6:00000000 r5:c74685a8 r4:c7a9f5a0
  
  [&lt;c009c298&gt;] (__dentry_open+0x0/0x2b8) from [&lt;c009c614&gt;] (nameidata_to_filp+0x38/0x50)
  
  [&lt;c009c5dc&gt;] (nameidata_to_filp+0x0/0x50) from [&lt;c00aa6bc&gt;] (do_filp_open+0x348/0x6f4)
  
   r4:00000000
  
  [&lt;c00aa374&gt;] (do_filp_open+0x0/0x6f4) from [&lt;c009c128&gt;] (do_sys_open+0x5c/0x170)
  
  [&lt;c009c0cc&gt;] (do_sys_open+0x0/0x170) from [&lt;c009c274&gt;] (sys_open+0x24/0x28)
  
   r8:c0027ee4 r7:00000005 r6:0007121c r5:0007129c r4:0007121c
  
  [&lt;c009c250&gt;] (sys_open+0x0/0x28) from [&lt;c0027d40&gt;] (ret_fast_syscall+0x0/0x2c)
  Code: e59c4080 e59c8090 e3540000 159c308c (17943103)
  
  ---[ end trace b9a765ee07f8c06b ]---
  </code></pre>