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NFS: swap IO handling is slightly different for O_DIRECT IO

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[ Upstream commit 64158668ac8b31626a8ce48db4cad08496eb8340 ]

1/ Taking the i_rwsem for swap IO triggers lockdep warnings regarding
   possible deadlocks with "fs_reclaim".  These deadlocks could, I believe,
   eventuate if a buffered read on the swapfile was attempted.

   We don't need coherence with the page cache for a swap file, and
   buffered writes are forbidden anyway.  There is no other need for
   i_rwsem during direct IO.  So never take it for swap_rw()

2/ generic_write_checks() explicitly forbids writes to swap, and
   performs checks that are not needed for swap.  So bypass it
   for swap_rw().

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
NeilBrown
2022-03-07 10:41:44 +11:00
committed by Greg Kroah-Hartman
parent 4b6f122bdf
commit d4170a2821
3 changed files with 34 additions and 20 deletions
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4
fs/nfs/file.c
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@@ -161,7 +161,7 @@ nfs_file_read(struct kiocb *iocb, struct iov_iter *to)
ssize_t result;
if (iocb->ki_flags & IOCB_DIRECT)
return nfs_file_direct_read(iocb, to);
return nfs_file_direct_read(iocb, to, false);
dprintk("NFS: read(%pD2, %zu@%lu)\n",
iocb->ki_filp,
@@ -616,7 +616,7 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)
return result;
if (iocb->ki_flags & IOCB_DIRECT)
return nfs_file_direct_write(iocb, from);
return nfs_file_direct_write(iocb, from, false);
dprintk("NFS: write(%pD2, %zu@%Ld)\n",
file, iov_iter_count(from), (long long) iocb->ki_pos);