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vfs: grab the lock instead of blocking in __fd_install during resizing

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Explicit locking in the fallback case provides a safe state of the
table. Getting rid of blocking semantics makes __fd_install usable
again in non-sleepable contexts, which easies backporting efforts.

There is a side effect of slightly nicer assembly for the common case
as might_sleep can now be removed.

Signed-off-by: Mateusz Guzik <[email protected]>
Signed-off-by: Al Viro <[email protected]>
This commit is contained in:
Mateusz Guzik 2017-10-03 12:58:15 +02:00 • committed by Al Viro
commit c02b1a9b41
2 changed files with 7 additions and 8 deletions
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11
fs/file.c
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@ -592,13 +592,16 @@ void __fd_install(struct files_struct *files, unsigned int fd,
{
struct fdtable *fdt;
might_sleep();
rcu_read_lock_sched();
while (unlikely(files->resize_in_progress)) {
if (unlikely(files->resize_in_progress)) {
rcu_read_unlock_sched();
wait_event(files->resize_wait, !files->resize_in_progress);
rcu_read_lock_sched();
spin_lock(&files->file_lock);
fdt = files_fdtable(files);
BUG_ON(fdt->fd[fd] != NULL);
rcu_assign_pointer(fdt->fd[fd], file);
spin_unlock(&files->file_lock);
return;
}
/* coupled with smp_wmb() in expand_fdtable() */
smp_rmb();