Re: [PATCH v4 00/12] Change readahead API

[David Sterba]

On Sat, Feb 01, 2020 at 07:12:28AM -0800, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> 
> I would particularly value feedback on this from the gfs2 and ocfs2
> maintainers.  They have non-trivial changes, and a review on patch 5
> would be greatly appreciated.
> 
> This series adds a readahead address_space operation to eventually
> replace the readpages operation.  The key difference is that
> pages are added to the page cache as they are allocated (and
> then looked up by the filesystem) instead of passing them on a
> list to the readpages operation and having the filesystem add
> them to the page cache.  It's a net reduction in code for each
> implementation, more efficient than walking a list, and solves
> the direct-write vs buffered-read problem reported by yu kuai at
> https://lore.kernel.org/linux-fsdevel/20200116063601.39201-1-yukuai3@xxxxxxxxxx/
> 
> v4:
>  - Rebase on current Linus (a62aa6f7f50a ("Merge tag 'gfs2-for-5.6'"))

I've tried to test the patchset but haven't got very far, it crashes at boot
ritht after VFS mounts the root. The patches are from mailinglist, applied on
current master, bug I saw the same crash with the git branch in your
repo (probably v1).

(gdb) l *(ext4_mpage_readpages+0x1da/0xc20)
0xffffffff813753f0 is in ext4_mpage_readpages (fs/ext4/readpage.c:226).
221             return i_size_read(inode);
222     }
223
224     int ext4_mpage_readpages(struct address_space *mapping, pgoff_t start,
225                     struct page *page, unsigned nr_pages, bool is_readahead)
226     {
227             struct bio *bio = NULL;
228             sector_t last_block_in_bio = 0;
229
230             struct inode *inode = mapping->host;

[    8.008531] BUG: kernel NULL pointer dereference, address: 0000000000000000
[    8.011482] #PF: supervisor read access in kernel mode
[    8.014121] #PF: error_code(0x0000) - not-present page
[    8.016767] PGD 0 P4D 0
[    8.018352] Oops: 0000 [#1] SMP
[    8.019716] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.5.0-default+ #955
[    8.021746] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014
[    8.025244] RIP: 0010:ext4_mpage_readpages+0x1da/0xc20
[    8.026817] Code: 7c 24 4e 00 0f 85 23 04 00 00 44 29 74 24 3c 83 6c 24 48 01 0f 84 4d 04 00 00 80 7c 24 4e 00 0f 85 fc 05 00 00 48 8b 4c 24 18 <48> 8b 01 f6 c4 20 75 89 4c 8b 69 20 b9 0c 00 00 00 2b 4c 24 38 83
[    8.031957] RSP: 0000:ffffb34f40013988 EFLAGS: 00010292
[    8.033691] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[    8.035533] RDX: 0000000000000001 RSI: ffffffff960934c0 RDI: ffffffff9681a080
[    8.036900] RBP: 0000000000000001 R08: ffffb34f40013a68 R09: 0000000000000000
[    8.038461] R10: 0000000000000038 R11: 0000000000000000 R12: 0000000000000004
[    8.040698] R13: ffff9668ba4e18e0 R14: 0000000000000001 R15: 0000000000000000
[    8.042805] FS:  0000000000000000(0000) GS:ffff9668bda00000(0000) knlGS:0000000000000000
[    8.045396] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    8.047233] CR2: 0000000000000000 CR3: 000000002e011001 CR4: 0000000000160ee0
[    8.049337] Call Trace:
[    8.050435]  ? __lock_acquire+0xee0/0x1320
[    8.051833]  ? release_pages+0x310/0x380
[    8.053265]  ? mark_held_locks+0x50/0x80
[    8.054468]  ext4_readahead+0x3b/0x50
[    8.055877]  read_pages+0x65/0x1a0
[    8.057167]  ? put_pages_list+0x90/0x90
[    8.058689]  __do_page_cache_readahead+0x24b/0x2a0
[    8.060394]  generic_file_buffered_read+0x7cf/0x9f0
[    8.062137]  ? sched_clock+0x5/0x10
[    8.063451]  ? up_read+0x18/0x240
[    8.064774]  ? ext4_xattr_get+0x97/0x2c0
[    8.066178]  new_sync_read+0x111/0x1a0
[    8.067423]  vfs_read+0xc5/0x180
[    8.068572]  kernel_read+0x2c/0x40
[    8.069788]  prepare_binprm+0x171/0x1b0
[    8.071311]  load_script+0x1c1/0x250
[    8.072643]  search_binary_handler+0x5f/0x210
[    8.074135]  exec_binprm+0xd7/0x290
[    8.075463]  __do_execve_file.isra.0+0x570/0x800
[    8.077400]  ? rest_init+0x2f1/0x2f5
[    8.078979]  do_execve+0x21/0x30
[    8.080420]  kernel_init+0xa4/0x11b
[    8.081856]  ? rest_init+0x2f5/0x2f5
[    8.083173]  ret_from_fork+0x24/0x30
[    8.084695] Modules linked in:
[    8.086055] CR2: 0000000000000000
[    8.087572] ---[ end trace 0890c371a706b34a ]---
[    8.089417] RIP: 0010:ext4_mpage_readpages+0x1da/0xc20
[    8.116836] BUG: sleeping function called from invalid context at include/linux/percpu-rwsem.h:38
[    8.119626] in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 1, name: swapper/0
[    8.122392] INFO: lockdep is turned off.
[    8.123694] irq event stamp: 18341344
[    8.124735] hardirqs last  enabled at (18341343): [<ffffffff95230c42>] free_unref_page_list+0x232/0x270
[    8.127918] hardirqs last disabled at (18341344): [<ffffffff95002b4b>] trace_hardirqs_off_thunk+0x1a/0x1c
[    8.131145] softirqs last  enabled at (18341250): [<ffffffff95a00358>] __do_softirq+0x358/0x52b
[    8.143060] softirqs last disabled at (18341243): [<ffffffff9508ae3d>] irq_exit+0x9d/0xb0
[    8.145603] CPU: 2 PID: 1 Comm: swapper/0 Tainted: G      D           5.5.0-default+ #955
[    8.148474] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014
[    8.152440] Call Trace:
[    8.153747]  dump_stack+0x71/0xa0
[    8.155238]  ___might_sleep.cold+0xa6/0xf9
[    8.156903]  exit_signals+0x31/0x310
[    8.158431]  ? __do_execve_file.isra.0+0x570/0x800
[    8.160179]  do_exit+0xa8/0xd60
[    8.161632]  ? rest_init+0x2f1/0x2f5
[    8.163204]  rewind_stack_do_exit+0x17/0x20
[    8.164931] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
[    8.167575] Kernel Offset: 0x14000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)