5.10-stable review patch. If anyone has any objections, please let me know.
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From: Eric W. Biederman ebiederm@xmission.com
[ Upstream commit b48845af0152d790a54b8ab78cc2b7c07485fc98 ]
Use the helper fget_task to simplify bpf_task_fd_query.
As well as simplifying the code this removes one unnecessary increment of struct files_struct. This unnecessary increment of files_struct.count can result in exec unnecessarily unsharing files_struct and breaking posix locks, and it can result in fget_light having to fallback to fget reducing performance.
This simplification comes from the observation that none of the callers of get_files_struct actually need to call get_files_struct that was made when discussing[1] exec and posix file locks.
[1] https://lkml.kernel.org/r/20180915160423.GA31461@redhat.com Suggested-by: Oleg Nesterov oleg@redhat.com v1: https://lkml.kernel.org/r/20200817220425.9389-5-ebiederm@xmission.com Link: https://lkml.kernel.org/r/20201120231441.29911-5-ebiederm@xmission.com Signed-off-by: Eric W. Biederman ebiederm@xmission.com Signed-off-by: Chuck Lever chuck.lever@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/syscall.c | 20 +++----------------- 1 file changed, 3 insertions(+), 17 deletions(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index e1bee8cd34044..fbe7f8e2b022c 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3929,7 +3929,6 @@ static int bpf_task_fd_query(const union bpf_attr *attr, pid_t pid = attr->task_fd_query.pid; u32 fd = attr->task_fd_query.fd; const struct perf_event *event; - struct files_struct *files; struct task_struct *task; struct file *file; int err; @@ -3949,23 +3948,11 @@ static int bpf_task_fd_query(const union bpf_attr *attr, if (!task) return -ENOENT;
- files = get_files_struct(task); - put_task_struct(task); - if (!files) - return -ENOENT; - err = 0; - spin_lock(&files->file_lock); - file = fcheck_files(files, fd); + file = fget_task(task, fd); + put_task_struct(task); if (!file) - err = -EBADF; - else - get_file(file); - spin_unlock(&files->file_lock); - put_files_struct(files); - - if (err) - goto out; + return -EBADF;
if (file->f_op == &bpf_link_fops) { struct bpf_link *link = file->private_data; @@ -4005,7 +3992,6 @@ static int bpf_task_fd_query(const union bpf_attr *attr, err = -ENOTSUPP; put_file: fput(file); -out: return err; }