[Devel] [PATCH 0/4] fix deadlock between synchronous reqs and fuse_invalidate_files

[Pavel Butsykin]

One more deadlock with fuse_invalidate_files():

[<ffffffff92ba7cc4>] __lock_page+0x74/0x90
[<ffffffff92bb9a75>] invalidate_inode_pages2_range+0x445/0x470
[<ffffffff92bb9ab7>] invalidate_inode_pages2+0x17/0x20
[<ffffffffc034cde5>] fuse_invalidate_files+0x235/0x270 [fuse]
[<ffffffffc033d3fb>] fuse_dev_do_write+0x7fb/0xe20 [fuse]
[<ffffffffc033ddc1>] fuse_dev_write+0x71/0xa0 [fuse]
[<ffffffff92c3c2e6>] do_sync_write+0x96/0xe0
[<ffffffff92c3cdc0>] vfs_write+0xc0/0x1f0
[<ffffffff92c3dbef>] SyS_write+0x7f/0xf0
[<ffffffff9315589b>] system_call_fastpath+0x22/0x27

This happened because synchronous kio read request was not dropped by kill_requests:

PID: 20684  TASK: ffff9543c2e71160  CPU: 5   COMMAND: "co_io"
[ffff9547b0faf9f8] __schedule at ffffffff93148a9f
[ffff9547b0fafa88] schedule at ffffffff93148fe9
[ffff9547b0fafa98] kpcs_req_send at ffffffffc047dab5 [fuse_kio_pcs]
[ffff9547b0fafb08] __fuse_request_send at ffffffffc033a987 [fuse]
[ffff9547b0fafb40] fuse_request_check_and_send at ffffffffc033e097 [fuse]
[ffff9547b0fafb50] fuse_send_read at ffffffffc03463ec [fuse]
[ffff9547b0fafb90] __fuse_readpage at ffffffffc03475ad [fuse]
[ffff9547b0fafc40] fuse_readpage at ffffffffc0347a3c [fuse]
[ffff9547b0fafca0] generic_file_read_iter at ffffffff92baa186
[ffff9547b0fafd58] generic_file_aio_read at ffffffff92baa5c5
[ffff9547b0fafdc0] fuse_file_aio_read at ffffffffc0343788 [fuse]
[ffff9547b0fafdf0] do_sync_read at ffffffff92c3c206
[ffff9547b0fafed0] vfs_read at ffffffff92c3cc2f
[ffff9547b0faff00] sys_pread64 at ffffffff92c3dcf2
[ffff9547b0faff50] system_call_fastpath at ffffffff9315589b 

 struct pcs_fuse_req {
 req = {
    list = {
      next = 0xffff95479374eb18,
      prev = 0xffff9547acf76e00
    },
    ...
    page_cache = 1,
    page_needs_release = 0,
    killed = 0,
    ...
    ff = 0x0,
    io_inode = 0xffff95445da0b740,

The fuse_file pointer was not initialized in req->ff, that means we can't check
ff->ff_state inside pcs_fuse_submit(), despite the fact that this request has
locked pages. It's believed that requests with an empty req->ff don't have pages,
therefore, such requests may not be synchronized with fuse_invalidate_files().
However, synchronous requests don't reference ff, but pass it as a parameter to
fuse_request_check_and_send(). 

This patchset fixes it.

Pavel Butsykin (4):
  fs/fuse kio: forward fuse_file pointer to kpcs_req_send()
  fs/fuse kio: add pending kio requests to kqueue
  fs/fuse kio: style fix in pcs_fuse_submit()
  fs/fuse kio: keep fuse_file for requests waiting for shrink

 fs/fuse/dev.c                      |   6 +-
 fs/fuse/file.c                     |   1 +
 fs/fuse/fuse_i.h                   |   4 +-
 fs/fuse/kio/pcs/fuse_io.c          |   5 ++
 fs/fuse/kio/pcs/pcs_fuse_kdirect.c | 120 +++++++++++++++++++++++++------------
 5 files changed, 93 insertions(+), 43 deletions(-)

-- 
2.15.1