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authorLinus Torvalds <torvalds@linux-foundation.org>2018-06-28 09:43:44 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-06-28 10:40:47 -0700
commita11e1d432b51f63ba698d044441284a661f01144 (patch)
tree9f3c5a10bf0d7f9a342d5fb39c0c35ea14170124 /Documentation
parentf57494321cbf5b1e7769b6135407d2995a369e28 (diff)
downloadlinux-a11e1d432b51f63ba698d044441284a661f01144.tar.gz
Revert changes to convert to ->poll_mask() and aio IOCB_CMD_POLL
The poll() changes were not well thought out, and completely unexplained. They also caused a huge performance regression, because "->poll()" was no longer a trivial file operation that just called down to the underlying file operations, but instead did at least two indirect calls. Indirect calls are sadly slow now with the Spectre mitigation, but the performance problem could at least be largely mitigated by changing the "->get_poll_head()" operation to just have a per-file-descriptor pointer to the poll head instead. That gets rid of one of the new indirections. But that doesn't fix the new complexity that is completely unwarranted for the regular case. The (undocumented) reason for the poll() changes was some alleged AIO poll race fixing, but we don't make the common case slower and more complex for some uncommon special case, so this all really needs way more explanations and most likely a fundamental redesign. [ This revert is a revert of about 30 different commits, not reverted individually because that would just be unnecessarily messy - Linus ] Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/Locking7
-rw-r--r--Documentation/filesystems/vfs.txt13
2 files changed, 1 insertions, 19 deletions
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 2c391338c675..37bf0a9de75c 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -441,8 +441,6 @@ prototypes:
int (*iterate) (struct file *, struct dir_context *);
int (*iterate_shared) (struct file *, struct dir_context *);
__poll_t (*poll) (struct file *, struct poll_table_struct *);
- struct wait_queue_head * (*get_poll_head)(struct file *, __poll_t);
- __poll_t (*poll_mask) (struct file *, __poll_t);
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
@@ -473,7 +471,7 @@ prototypes:
};
locking rules:
- All except for ->poll_mask may block.
+ All may block.
->llseek() locking has moved from llseek to the individual llseek
implementations. If your fs is not using generic_file_llseek, you
@@ -505,9 +503,6 @@ in sys_read() and friends.
the lease within the individual filesystem to record the result of the
operation
-->poll_mask can be called with or without the waitqueue lock for the waitqueue
-returned from ->get_poll_head.
-
--------------------------- dquot_operations -------------------------------
prototypes:
int (*write_dquot) (struct dquot *);
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 829a7b7857a4..f608180ad59d 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -857,8 +857,6 @@ struct file_operations {
ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
int (*iterate) (struct file *, struct dir_context *);
__poll_t (*poll) (struct file *, struct poll_table_struct *);
- struct wait_queue_head * (*get_poll_head)(struct file *, __poll_t);
- __poll_t (*poll_mask) (struct file *, __poll_t);
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
@@ -903,17 +901,6 @@ otherwise noted.
activity on this file and (optionally) go to sleep until there
is activity. Called by the select(2) and poll(2) system calls
- get_poll_head: Returns the struct wait_queue_head that callers can
- wait on. Callers need to check the returned events using ->poll_mask
- once woken. Can return NULL to indicate polling is not supported,
- or any error code using the ERR_PTR convention to indicate that a
- grave error occured and ->poll_mask shall not be called.
-
- poll_mask: return the mask of EPOLL* values describing the file descriptor
- state. Called either before going to sleep on the waitqueue returned by
- get_poll_head, or after it has been woken. If ->get_poll_head and
- ->poll_mask are implemented ->poll does not need to be implement.
-
unlocked_ioctl: called by the ioctl(2) system call.
compat_ioctl: called by the ioctl(2) system call when 32 bit system calls