btrfs: fix deadlock due to page faults during direct IO reads and writes
commit 51bd9563 upstream 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 c03098d4 ("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> Signed-off-by:
Anand Jain <anand.jain@oracle.com> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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