On Mon, Nov 25, 2019 at 10:39:49PM +0000, David Howells wrote: > David Howells (12): > pipe: Reduce #inclusion of pipe_fs_i.h > Remove the nr_exclusive argument from __wake_up_sync_key() > Add wake_up_interruptible_sync_poll_locked() > pipe: Use head and tail pointers for the ring, not cursor and length This commit (8cefc107ca54c8b06438b7dc9) causes hangs of 'btrfs send' commands, that's eg. inside fstests or in btrfs-progs testsuite. The 'send' uses pipe/splice to get data from kernel to userspace. The test that reliably worked for me leaves the process hanging with this stacktrace (no CPU or IO activity): [<0>] pipe_write+0x1be/0x4b0 [<0>] new_sync_write+0x11e/0x1c0 [<0>] vfs_write+0xc1/0x1d0 [<0>] kernel_write+0x2c/0x40 [<0>] send_cmd+0x78/0xf0 [btrfs] [<0>] send_extent_data+0x4b1/0x52c [btrfs] [<0>] process_extent+0xe46/0xe9d [btrfs] [<0>] changed_cb+0xcf5/0xd2f [btrfs] [<0>] send_subvol+0x8ad/0xc0b [btrfs] [<0>] btrfs_ioctl_send+0xe50/0xf30 [btrfs] [<0>] _btrfs_ioctl_send+0x80/0x110 [btrfs] [<0>] btrfs_ioctl+0x18e1/0x3450 [btrfs] [<0>] do_vfs_ioctl+0xa5/0x710 [<0>] ksys_ioctl+0x70/0x80 [<0>] __x64_sys_ioctl+0x16/0x20 [<0>] do_syscall_64+0x56/0x220 [<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe I've bisected that to the mentioned commit, using test in btrfs-progs testsuite with command "make TEST=016\* test-misc". Normally the test can run up to 10 seconds, in the buggy case it stays there. I can help testing fixes or gathering more information, please let me know. Full bisect log: # bad: [3c0edea9b29f9be6c093f236f762202b30ac9431] pipe: Remove sync on wake_ups # good: [da0c9ea146cbe92b832f1b0f694840ea8eb33cce] Linux 5.4-rc2 git bisect start '3c0edea9b29f9be6c093f236f762202b30ac9431' 'd055b4fb4d165b06d912e7f846610d120c3bb9fb^' # bad: [b667b867344301e24f21d4a4c844675ff61d89e1] pipe: Advance tail pointer inside of wait spinlock in pipe_read() git bisect bad b667b867344301e24f21d4a4c844675ff61d89e1 # good: [f94df9890e98f2090c6a8d70c795134863b70201] Add wake_up_interruptible_sync_poll_locked() git bisect good f94df9890e98f2090c6a8d70c795134863b70201 # bad: [6718b6f855a0b4962d54bd625be2718cb820cec6] pipe: Allow pipes to have kernel-reserved slots git bisect bad 6718b6f855a0b4962d54bd625be2718cb820cec6 # bad: [8cefc107ca54c8b06438b7dc9cc08bc0a11d5b98] pipe: Use head and tail pointers for the ring, not cursor and length git bisect bad 8cefc107ca54c8b06438b7dc9cc08bc0a11d5b98 # first bad commit: [8cefc107ca54c8b06438b7dc9cc08bc0a11d5b98] pipe: Use head and tail pointers for the ring, not cursor and length > pipe: Allow pipes to have kernel-reserved slots > pipe: Advance tail pointer inside of wait spinlock in pipe_read() > pipe: Conditionalise wakeup in pipe_read() > pipe: Rearrange sequence in pipe_write() to preallocate slot > pipe: Remove redundant wakeup from pipe_write() > pipe: Check for ring full inside of the spinlock in pipe_write() > pipe: Increase the writer-wakeup threshold to reduce context-switch count > pipe: Remove sync on wake_ups
