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Filipe Manana 51bd9563b6 btrfs: fix deadlock due to page faults during direct IO reads and writes 
If we do a direct IO read or write when the buffer given by the user is
memory mapped to the file range we are going to do IO, we end up ending
in a deadlock. This is triggered by the new test case generic/647 from
fstests.

For a direct IO read we get a trace like this:

  [967.872718] INFO: task mmap-rw-fault:12176 blocked for more than 120 seconds.
  [967.874161]       Not tainted 5.14.0-rc7-btrfs-next-95 #1
  [967.874909] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  [967.875983] task:mmap-rw-fault   state:D stack:    0 pid:12176 ppid: 11884 flags:0x00000000
  [967.875992] Call Trace:
  [967.875999]  __schedule+0x3ca/0xe10
  [967.876015]  schedule+0x43/0xe0
  [967.876020]  wait_extent_bit.constprop.0+0x1eb/0x260 [btrfs]
  [967.876109]  ? do_wait_intr_irq+0xb0/0xb0
  [967.876118]  lock_extent_bits+0x37/0x90 [btrfs]
  [967.876150]  btrfs_lock_and_flush_ordered_range+0xa9/0x120 [btrfs]
  [967.876184]  ? extent_readahead+0xa7/0x530 [btrfs]
  [967.876214]  extent_readahead+0x32d/0x530 [btrfs]
  [967.876253]  ? lru_cache_add+0x104/0x220
  [967.876255]  ? kvm_sched_clock_read+0x14/0x40
  [967.876258]  ? sched_clock_cpu+0xd/0x110
  [967.876263]  ? lock_release+0x155/0x4a0
  [967.876271]  read_pages+0x86/0x270
  [967.876274]  ? lru_cache_add+0x125/0x220
  [967.876281]  page_cache_ra_unbounded+0x1a3/0x220
  [967.876291]  filemap_fault+0x626/0xa20
  [967.876303]  __do_fault+0x36/0xf0
  [967.876308]  __handle_mm_fault+0x83f/0x15f0
  [967.876322]  handle_mm_fault+0x9e/0x260
  [967.876327]  __get_user_pages+0x204/0x620
  [967.876332]  ? get_user_pages_unlocked+0x69/0x340
  [967.876340]  get_user_pages_unlocked+0xd3/0x340
  [967.876349]  internal_get_user_pages_fast+0xbca/0xdc0
  [967.876366]  iov_iter_get_pages+0x8d/0x3a0
  [967.876374]  bio_iov_iter_get_pages+0x82/0x4a0
  [967.876379]  ? lock_release+0x155/0x4a0
  [967.876387]  iomap_dio_bio_actor+0x232/0x410
  [967.876396]  iomap_apply+0x12a/0x4a0
  [967.876398]  ? iomap_dio_rw+0x30/0x30
  [967.876414]  __iomap_dio_rw+0x29f/0x5e0
  [967.876415]  ? iomap_dio_rw+0x30/0x30
  [967.876420]  ? lock_acquired+0xf3/0x420
  [967.876429]  iomap_dio_rw+0xa/0x30
  [967.876431]  btrfs_file_read_iter+0x10b/0x140 [btrfs]
  [967.876460]  new_sync_read+0x118/0x1a0
  [967.876472]  vfs_read+0x128/0x1b0
  [967.876477]  __x64_sys_pread64+0x90/0xc0
  [967.876483]  do_syscall_64+0x3b/0xc0
  [967.876487]  entry_SYSCALL_64_after_hwframe+0x44/0xae
  [967.876490] RIP: 0033:0x7fb6f2c038d6
  [967.876493] RSP: 002b:00007fffddf586b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000011
  [967.876496] RAX: ffffffffffffffda RBX: 0000000000001000 RCX: 00007fb6f2c038d6
  [967.876498] RDX: 0000000000001000 RSI: 00007fb6f2c17000 RDI: 0000000000000003
  [967.876499] RBP: 0000000000001000 R08: 0000000000000003 R09: 0000000000000000
  [967.876501] R10: 0000000000001000 R11: 0000000000000246 R12: 0000000000000003
  [967.876502] R13: 0000000000000000 R14: 00007fb6f2c17000 R15: 0000000000000000

This happens because at btrfs_dio_iomap_begin() we lock the extent range
and return with it locked - we only unlock in the endio callback, at
end_bio_extent_readpage() -> endio_readpage_release_extent(). Then after
iomap called the btrfs_dio_iomap_begin() callback, it triggers the page
faults that resulting in reading the pages, through the readahead callback
btrfs_readahead(), and through there we end to attempt to lock again the
same extent range (or a subrange of what we locked before), resulting in
the deadlock.

For a direct IO write, the scenario is a bit different, and it results in
trace like this:

  [1132.442520] run fstests generic/647 at 2021-08-31 18:53:35
  [1330.349355] INFO: task mmap-rw-fault:184017 blocked for more than 120 seconds.
  [1330.350540]       Not tainted 5.14.0-rc7-btrfs-next-95 #1
  [1330.351158] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  [1330.351900] task:mmap-rw-fault   state:D stack:    0 pid:184017 ppid:183725 flags:0x00000000
  [1330.351906] Call Trace:
  [1330.351913]  __schedule+0x3ca/0xe10
  [1330.351930]  schedule+0x43/0xe0
  [1330.351935]  btrfs_start_ordered_extent+0x108/0x1c0 [btrfs]
  [1330.352020]  ? do_wait_intr_irq+0xb0/0xb0
  [1330.352028]  btrfs_lock_and_flush_ordered_range+0x8c/0x120 [btrfs]
  [1330.352064]  ? extent_readahead+0xa7/0x530 [btrfs]
  [1330.352094]  extent_readahead+0x32d/0x530 [btrfs]
  [1330.352133]  ? lru_cache_add+0x104/0x220
  [1330.352135]  ? kvm_sched_clock_read+0x14/0x40
  [1330.352138]  ? sched_clock_cpu+0xd/0x110
  [1330.352143]  ? lock_release+0x155/0x4a0
  [1330.352151]  read_pages+0x86/0x270
  [1330.352155]  ? lru_cache_add+0x125/0x220
  [1330.352162]  page_cache_ra_unbounded+0x1a3/0x220
  [1330.352172]  filemap_fault+0x626/0xa20
  [1330.352176]  ? filemap_map_pages+0x18b/0x660
  [1330.352184]  __do_fault+0x36/0xf0
  [1330.352189]  __handle_mm_fault+0x1253/0x15f0
  [1330.352203]  handle_mm_fault+0x9e/0x260
  [1330.352208]  __get_user_pages+0x204/0x620
  [1330.352212]  ? get_user_pages_unlocked+0x69/0x340
  [1330.352220]  get_user_pages_unlocked+0xd3/0x340
  [1330.352229]  internal_get_user_pages_fast+0xbca/0xdc0
  [1330.352246]  iov_iter_get_pages+0x8d/0x3a0
  [1330.352254]  bio_iov_iter_get_pages+0x82/0x4a0
  [1330.352259]  ? lock_release+0x155/0x4a0
  [1330.352266]  iomap_dio_bio_actor+0x232/0x410
  [1330.352275]  iomap_apply+0x12a/0x4a0
  [1330.352278]  ? iomap_dio_rw+0x30/0x30
  [1330.352292]  __iomap_dio_rw+0x29f/0x5e0
  [1330.352294]  ? iomap_dio_rw+0x30/0x30
  [1330.352306]  btrfs_file_write_iter+0x238/0x480 [btrfs]
  [1330.352339]  new_sync_write+0x11f/0x1b0
  [1330.352344]  ? NF_HOOK_LIST.constprop.0.cold+0x31/0x3e
  [1330.352354]  vfs_write+0x292/0x3c0
  [1330.352359]  __x64_sys_pwrite64+0x90/0xc0
  [1330.352365]  do_syscall_64+0x3b/0xc0
  [1330.352369]  entry_SYSCALL_64_after_hwframe+0x44/0xae
  [1330.352372] RIP: 0033:0x7f4b0a580986
  [1330.352379] RSP: 002b:00007ffd34d75418 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
  [1330.352382] RAX: ffffffffffffffda RBX: 0000000000001000 RCX: 00007f4b0a580986
  [1330.352383] RDX: 0000000000001000 RSI: 00007f4b0a3a4000 RDI: 0000000000000003
  [1330.352385] RBP: 00007f4b0a3a4000 R08: 0000000000000003 R09: 0000000000000000
  [1330.352386] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
  [1330.352387] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Unlike for reads, at btrfs_dio_iomap_begin() we return with the extent
range unlocked, but later when the page faults are triggered and we try
to read the extents, we end up btrfs_lock_and_flush_ordered_range() where
we find the ordered extent for our write, created by the iomap callback
btrfs_dio_iomap_begin(), and we wait for it to complete, which makes us
deadlock since we can't complete the ordered extent without reading the
pages (the iomap code only submits the bio after the pages are faulted
in).

Fix this by setting the nofault attribute of the given iov_iter and retry
the direct IO read/write if we get an -EFAULT error returned from iomap.
For reads, also disable page faults completely, this is because when we
read from a hole or a prealloc extent, we can still trigger page faults
due to the call to iov_iter_zero() done by iomap - at the moment, it is
oblivious to the value of the ->nofault attribute of an iov_iter.
We also need to keep track of the number of bytes written or read, and
pass it to iomap_dio_rw(), as well as use the new flag IOMAP_DIO_PARTIAL.

This depends on the iov_iter and iomap changes introduced in commit
c03098d4b9 ("Merge tag 'gfs2-v5.15-rc5-mmap-fault' of
git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2").

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2021-11-09 13:46:07 +01:00
arch gfs2: Fix mmap + page fault deadlocks 2021-11-02 12:25:03 -07:00
block for-5.16/inode-sync-2021-10-29 2021-11-01 10:25:27 -07:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-11-01 21:24:02 -07:00
Documentation ARM: 2021-11-02 11:24:14 -07:00
drivers gfs2: Fix mmap + page fault deadlocks 2021-11-02 12:25:03 -07:00
fs btrfs: fix deadlock due to page faults during direct IO reads and writes 2021-11-09 13:46:07 +01:00
include gfs2: Fix mmap + page fault deadlocks 2021-11-02 12:25:03 -07:00
init Tracing updates for 5.16: 2021-11-01 20:05:19 -07:00
ipc ipc: remove memcg accounting for sops objects in do_semtimedop() 2021-09-14 10:22:11 -07:00
kernel printk changes for 5.16 2021-11-02 10:53:45 -07:00
lib gfs2: Fix mmap + page fault deadlocks 2021-11-02 12:25:03 -07:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm gfs2: Fix mmap + page fault deadlocks 2021-11-02 12:25:03 -07:00
net Core: 2021-11-02 06:20:58 -07:00
samples Core: 2021-11-02 06:20:58 -07:00
scripts ARM development for 5.16: 2021-11-02 11:33:15 -07:00
security integrity-v5.16 2021-11-02 10:51:28 -07:00
sound ALSA: usb-audio: Fix microphone sound on Jieli webcam. 2021-10-19 08:07:01 +02:00
tools ARM: 2021-11-02 11:24:14 -07:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt kvm: irqfd: avoid update unmodified entries of the routing 2021-09-30 04:27:10 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap media updates for v5.16-rc1 2021-11-01 18:45:08 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS ARM: 2021-11-02 11:24:14 -07:00
Makefile Core: 2021-11-02 06:20:58 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.