** Also affects: linux (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Also affects: linux (Ubuntu Trusty)
   Importance: Undecided
       Status: New

** Also affects: linux (Ubuntu Artful)
   Importance: Undecided
       Status: New

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1777029

Title:
  fscache: Fix hanging wait on page discarded by writeback

Status in linux package in Ubuntu:
  Confirmed
Status in linux source package in Trusty:
  New
Status in linux source package in Xenial:
  New
Status in linux source package in Artful:
  New
Status in linux source package in Bionic:
  New

Bug description:
  == SRU Justification ==

  [Impact]
  Under heavy NFS + FSCache load, a user sometimes observes a hang in 
__fscache_wait_on_page_write+0x5f/0xa0.

  Example traces:
  [<ffffffffc009f1bf>] __fscache_wait_on_page_write+0x5f/0xa0 [fscache]
  [<ffffffffc009f6da>] __fscache_uncache_all_inode_pages+0xba/0x120 [fscache]
  [<ffffffffc0419ece>] nfs_fscache_open_file+0x4e/0xc0 [nfs]

  [<ffffffffc034f1bf>] __fscache_wait_on_page_write+0x5f/0xa0 [fscache]
  [<ffffffffc04104dc>] __nfs_fscache_invalidate_page+0x2c/0x80 [nfs]
  [<ffffffffc03fb543>] nfs_invalidate_page+0x63/0x90 [nfs]
  [<ffffffff811925c0>] truncate_inode_page+0x80/0x90

  [Fix]
  Cherry-pick 2c98425720233ae3e135add0c7e869b32913502f from upstream, which is 
a patch from the FSCache maintainer.

  [Testcase]
  The user has run a NFS stress-test with a similar home-grown patch, and will 
run a stress test on the proposed kernel.

  [Regression Potential]
  Patch is limited to FSCache, so regression potential is limited.

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