Kernel panic on a RHEL5.4 NFS client in `blockable_page_cache_readahead` code.

Issue

• A RHEL5.4 machine faces a kernel panic with the following messages :

Unable to handle kernel NULL pointer dereference at 0000000000000f58 RIP: 
 [<0000000000000f58>]
PGD 80e3cf067 PUD 823092067 PMD 2ee060067 PTE 0
Oops: 0010 [1] SMP 
last sysfs file: /class/net/lo/operstate
CPU 0 
Modules linked in: nfs fscache nfs_acl autofs4 vsock(U) vmmemctl(U) pvscsi(U) acpiphp lockd sunrpc dm_mirror dm_multipath scsi_dh video hwmon backlight sbs i2c_ec button battery asus_acpi acpi_memhotplug ac lp floppy sg i2c_piix4 i2c_core vmci(U) pcspkr e1000 shpchp parport_pc parport serio_raw ide_cd cdrom vmxnet(U) dm_raid45 dm_message dm_region_hash dm_log dm_mod dm_mem_cache ata_piix libata mptspi mptscsih mptbase scsi_transport_spi sd_mod scsi_mod ext3 jbd uhci_hcd ohci_hcd ehci_hcd
Pid: 24036, comm: network_speed_m Tainted: G      2.6.18-164.10.1.el5 #1
RIP: 0010:[<0000000000000f58>]  [<0000000000000f58>]
RSP: 0018:ffff8102ec2d7c10  EFLAGS: 00010202
RAX: ffff8108369d5240 RBX: ffff8102ec2d7ce8 RCX: 0000000000000010
RDX: 0000000000000f58 RSI: 0000000000000004 RDI: 00000000000010f8
RBP: ffff8102f27979c0 R08: ffff8102ec2d7ce8 R09: 0000000000000000
R10: 000000000001bb90 R11: 0000000000000000 R12: 0000000000000010
R13: 0000000000000004 R14: ffff8102ed40bcc0 R15: ffff8102ec2d7e88
FS:  0000000000000000(0000) GS:ffffffff803c1000(0063) knlGS:00000000f7f0f6c0
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000f58 CR3: 00000002f2cf1000 CR4: 00000000000006e0
Process network_speed_m (pid: 24036, threadinfo ffff8102ec2d6000, task ffff8102ea0c9820)
Stack:  ffffffff8003243f ffff8102ec2d7ce8 0000000000000000 0000000000000001
 ffff8102ed40bcc0 ffff8102f27979c0 ffffffff8002ee32 0000000000010246
 ffff8102ec2d7ce8 000000000001bb90 ffffffff80013f81 ffff8102ec2d7de8
Call Trace:
 [<ffffffff8003243f>] blockable_page_cache_readahead+0x34/0xb2
 [<ffffffff8002ee32>] make_ahead_window+0x82/0x9e
 [<ffffffff80013f81>] page_cache_readahead+0x156/0x1af
 [<ffffffff8000c189>] do_generic_mapping_read+0xc6/0x354
 [<ffffffff8000d0b6>] file_read_actor+0x0/0x159
 [<ffffffff8000c563>] __generic_file_aio_read+0x14c/0x198
 [<ffffffff80016ccd>] generic_file_aio_read+0x34/0x39
 [<ffffffff8000cddf>] do_sync_read+0xc7/0x104
 [<ffffffff80066b58>] do_page_fault+0x4fe/0x830
 [<ffffffff8009fdcf>] autoremove_wake_function+0x0/0x2e
 [<ffffffff80062fc8>] thread_return+0x62/0xfe
 [<ffffffff8000b695>] vfs_read+0xcb/0x171
 [<ffffffff80011b72>] sys_read+0x45/0x6e
 [<ffffffff8006149d>] sysenter_do_call+0x1e/0x6a


Code:  Bad RIP value.
RIP  [<0000000000000f58>]
 RSP <ffff8102ec2d7c10>