search for: extent_range_uptod

A user has encountered a NULL pointer kernel oops in btrfs when encountering media errors. The problem has been identified as an unhandled NULL pointer returned from find_get_page(). This modification simply checks for a NULL page, and returns with an error if found (the extent_range_uptodate() function returns 1 on errors). After testing this patch, the user reported that the error with the NULL pointer oops was solved. However, there is still a remaining problem with a thread becoming stuck in wait_on_page_locked(page) in the read_extent_buffer_pages(...) function in extent_io.c...

...evid 1 transid 4 /dev/zd0 Aug 31 20:30:34 DELL kernel: [34328.134001] btrfs: disk space caching is enabled Aug 31 20:30:34 DELL kernel: [34328.135701] BUG: unable to handle kernel NULL pointer dereference at (null) Aug 31 20:30:34 DELL kernel: [34328.137200] IP: [<ffffffffa0068439>] extent_range_uptodate+0x59/0xe0 [btrfs] Aug 31 20:30:34 DELL kernel: [34328.138759] PGD 0 Aug 31 20:30:34 DELL kernel: [34328.140248] Oops: 0000 [#1] SMP Aug 31 20:30:34 DELL kernel: [34328.141777] CPU 3 Aug 31 20:30:34 DELL kernel: [34328.141811] Modules linked in: ses enclosure ppp_mppe ppp_async crc_ccitt pci_stub...

...ffa0325e6f ffff8800307776c0 ffff88001c9f3d78 ffff8800335d3000 [44121.745517] ffff88001c9f3d78 ffff880032c46280 ffffffffa0307bc0 ffff8800337721c0 [44121.745567] ffff880032c46280 ffff880032c46280 ffffffffa032ccf5 0000000000000000 [44121.745616] Call Trace: [44121.745941] [<ffffffffa0325e6f>] extent_range_uptodate+0x71/0xa1 [btrfs] [44121.746260] [<ffffffffa0307bc0>] end_workqueue_fn+0x23/0x67 [btrfs] [44121.746457] [<ffffffffa032ccf5>] worker_loop+0x92/0x2ad [btrfs] [44121.746751] [<ffffffff81056d59>] kthread+0x76/0x7e [44121.746787] [<ffffffff813d2234>] kernel_thread_helper+0...

...ad(10): 28 00 70 2f dc 5f 00 00 08 00 [ 141.952293] end_request: I/O error, dev sdd, sector 1882184801 [ 141.952313] ata6: EH complete [ 141.952335] BUG: unable to handle kernel NULL pointer dereference at (null) [ 141.952383] IP: [<ffffffffa018e439>] extent_range_uptodate+0x59/0xe0 [btrfs] [ 141.952440] PGD 21caae067 PUD 221e55067 PMD 0 [ 141.952466] Oops: 0000 [#1] SMP [ 141.952485] CPU 1 [ 141.952496] Modules linked in: ip6table_filter ip6_tables rfcomm bnep bluetooth ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 nf_defrag_ipv4...

For quite a while, I''ve experienced oddities with snapshotted Firefox _CACHE_00?_ files, whose checksums (and contents) would change after the btrfs snapshot was taken, and would even change depending on how the file was brought to memory (e.g., rsyncing it to backup storage vs checking its md5sum before or after the rsync). This only affected these cache files, so I didn''t give