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NFS: swap IO handling is slightly different for O_DIRECT IO

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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>
This commit is contained in:
NeilBrown
2022-03-07 10:41:44 +11:00
committed by Trond Myklebust
parent 4dc73c6791
commit 64158668ac
3 changed files with 34 additions and 20 deletions
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8
include/linux/nfs_fs.h
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@@ -508,10 +508,10 @@ static inline const struct cred *nfs_file_cred(struct file *file)
* linux/fs/nfs/direct.c
*/
extern ssize_t nfs_direct_IO(struct kiocb *, struct iov_iter *);
extern ssize_t nfs_file_direct_read(struct kiocb *iocb,
struct iov_iter *iter);
extern ssize_t nfs_file_direct_write(struct kiocb *iocb,
struct iov_iter *iter);
ssize_t nfs_file_direct_read(struct kiocb *iocb,
struct iov_iter *iter, bool swap);
ssize_t nfs_file_direct_write(struct kiocb *iocb,
struct iov_iter *iter, bool swap);
/*
* linux/fs/nfs/dir.c