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Revert "fget: clarify and improve __fget_files() implementation"

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Temporarily revert commit 0849f83e47 ("fget: clarify and improve
__fget_files() implementation") to enable subsequent upstream
commits to apply and build cleanly.

Stable-dep-of: bebf684bf330 ("file: Rename __fcheck_files to files_lookup_fd_raw")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Chuck Lever
2024-02-29 18:19:36 -05:00
committed by Greg Kroah-Hartman
parent 4d037e1173
commit e6f42bc11a
1 changed files with 16 additions and 56 deletions
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72
fs/file.c
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@@ -849,68 +849,28 @@ void do_close_on_exec(struct files_struct *files)
spin_unlock(&files->file_lock); spin_unlock(&files->file_lock);
} }
static inline struct file *__fget_files_rcu(struct files_struct *files,
unsigned int fd, fmode_t mask, unsigned int refs)
{
for (;;) {
struct file *file;
struct fdtable *fdt = rcu_dereference_raw(files->fdt);
struct file __rcu **fdentry;
if (unlikely(fd >= fdt->max_fds))
return NULL;
fdentry = fdt->fd + array_index_nospec(fd, fdt->max_fds);
file = rcu_dereference_raw(*fdentry);
if (unlikely(!file))
return NULL;
if (unlikely(file->f_mode & mask))
return NULL;
/*
* Ok, we have a file pointer. However, because we do
* this all locklessly under RCU, we may be racing with
* that file being closed.
*
* Such a race can take two forms:
*
* (a) the file ref already went down to zero,
* and get_file_rcu_many() fails. Just try
* again:
*/
if (unlikely(!get_file_rcu_many(file, refs)))
continue;
/*
* (b) the file table entry has changed under us.
* Note that we don't need to re-check the 'fdt->fd'
* pointer having changed, because it always goes
* hand-in-hand with 'fdt'.
*
* If so, we need to put our refs and try again.
*/
if (unlikely(rcu_dereference_raw(files->fdt) != fdt) ||
unlikely(rcu_dereference_raw(*fdentry) != file)) {
fput_many(file, refs);
continue;
}
/*
* Ok, we have a ref to the file, and checked that it
* still exists.
*/
return file;
}
}
static struct file *__fget_files(struct files_struct *files, unsigned int fd, static struct file *__fget_files(struct files_struct *files, unsigned int fd,
fmode_t mask, unsigned int refs) fmode_t mask, unsigned int refs)
{ {
struct file *file; struct file *file;
rcu_read_lock(); rcu_read_lock();
file = __fget_files_rcu(files, fd, mask, refs); loop:
file = fcheck_files(files, fd);
if (file) {
/* File object ref couldn't be taken.
* dup2() atomicity guarantee is the reason
* we loop to catch the new file (or NULL pointer)
*/
if (file->f_mode & mask)
file = NULL;
else if (!get_file_rcu_many(file, refs))
goto loop;
else if (__fcheck_files(files, fd) != file) {
fput_many(file, refs);
goto loop;
}
}
rcu_read_unlock(); rcu_read_unlock();
return file; return file;