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| author | Eric W. Biederman <ebiederm@xmission.com> | 2020-11-21 00:14:34 +0100 |
|---|---|---|
| committer | Eric W. Biederman <ebiederm@xmission.com> | 2020-12-10 19:42:58 +0100 |
| commit | 775e0656b27210ae668e33af00bece858f44576f (patch) | |
| tree | 246ddc8786c491d3c13b3f96d5d7fa73625aaed3 | |
| parent | bpf/task_iter: In task_file_seq_get_next use task_lookup_next_fd_rcu (diff) | |
| download | linux-775e0656b27210ae668e33af00bece858f44576f.tar.xz linux-775e0656b27210ae668e33af00bece858f44576f.zip | |
proc/fd: In fdinfo seq_show don't use get_files_struct
When discussing[1] exec and posix file locks it was realized that none
of the callers of get_files_struct fundamentally needed to call
get_files_struct, and that by switching them to helper functions
instead it will both simplify their code and remove unnecessary
increments of files_struct.count. Those unnecessary increments can
result in exec unnecessarily unsharing files_struct which breaking
posix locks, and it can result in fget_light having to fallback to
fget reducing system performance.
Instead hold task_lock for the duration that task->files needs to be
stable in seq_show. The task_lock was already taken in
get_files_struct, and so skipping get_files_struct performs less work
overall, and avoids the problems with the files_struct reference
count.
[1] https://lkml.kernel.org/r/20180915160423.GA31461@redhat.com
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
v1: https://lkml.kernel.org/r/20200817220425.9389-12-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/20201120231441.29911-17-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
| -rw-r--r-- | fs/proc/fd.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/fs/proc/fd.c b/fs/proc/fd.c index 72c1525b4b3e..cb51763ed554 100644 --- a/fs/proc/fd.c +++ b/fs/proc/fd.c @@ -28,9 +28,8 @@ static int seq_show(struct seq_file *m, void *v) if (!task) return -ENOENT; - files = get_files_struct(task); - put_task_struct(task); - + task_lock(task); + files = task->files; if (files) { unsigned int fd = proc_fd(m->private); @@ -47,8 +46,9 @@ static int seq_show(struct seq_file *m, void *v) ret = 0; } spin_unlock(&files->file_lock); - put_files_struct(files); } + task_unlock(task); + put_task_struct(task); if (ret) return ret; @@ -57,6 +57,7 @@ static int seq_show(struct seq_file *m, void *v) (long long)file->f_pos, f_flags, real_mount(file->f_path.mnt)->mnt_id); + /* show_fd_locks() never deferences files so a stale value is safe */ show_fd_locks(m, file, files); if (seq_has_overflowed(m)) goto out; |