lkml.org 
[lkml]   [2020]   [Nov]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH v2 16/24] bpf/task_iter: In task_file_seq_get_next use task_lookup_next_fd_rcu
    From
    Date


    On 11/20/20 3:14 PM, Eric W. Biederman wrote:
    > 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.
    >
    > Using task_lookup_next_fd_rcu simplifies task_file_seq_get_next, by
    > moving the checking for the maximum file descritor into the generic
    > code, and by remvoing the need for capturing and releasing a reference
    > on files_struct. As the reference count of files_struct no longer
    > needs to be maintained bpf_iter_seq_task_file_info can have it's files
    > member removed and task_file_seq_get_next no longer needs it's fstruct
    > argument.
    >
    > The curr_fd local variable does need to become unsigned to be used
    > with fnext_task. As curr_fd is assigned from and assigned a u32
    > making curr_fd an unsigned int won't cause problems and might prevent
    > them.
    >
    > [1] https://lkml.kernel.org/r/20180915160423.GA31461@redhat.com
    > Suggested-by: Oleg Nesterov <oleg@redhat.com>
    > v1: https://lkml.kernel.org/r/20200817220425.9389-11-ebiederm@xmission.com
    > Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    > ---
    > kernel/bpf/task_iter.c | 44 ++++++++++--------------------------------
    > 1 file changed, 10 insertions(+), 34 deletions(-)


    Just a heads-up. The following patch
    bpf-next: 91b2db27d3ff ("bpf: Simplify task_file_seq_get_next()")

    https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=91b2db27d3ff9ad29e8b3108dfbf1e2f49fe9bd3
    has been merged in bpf-next tree.

    It will have merge conflicts with this patch. The above patch
    is a refactoring for simplification with no functionality change.

    >
    > diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
    > index 5ab2ccfb96cb..4ec63170c741 100644
    > --- a/kernel/bpf/task_iter.c
    > +++ b/kernel/bpf/task_iter.c
    > @@ -130,45 +130,33 @@ struct bpf_iter_seq_task_file_info {
    > */
    > struct bpf_iter_seq_task_common common;
    > struct task_struct *task;
    > - struct files_struct *files;
    > u32 tid;
    > u32 fd;
    > };
    >
    > static struct file *
    > task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info,
    > - struct task_struct **task, struct files_struct **fstruct)
    > + struct task_struct **task)
    > {
    > struct pid_namespace *ns = info->common.ns;
    > - u32 curr_tid = info->tid, max_fds;
    > - struct files_struct *curr_files;
    > + u32 curr_tid = info->tid;
    > struct task_struct *curr_task;
    > - int curr_fd = info->fd;
    > + unsigned int curr_fd = info->fd;
    >
    > /* If this function returns a non-NULL file object,
    > - * it held a reference to the task/files_struct/file.
    > + * it held a reference to the task/file.
    > * Otherwise, it does not hold any reference.
    > */
    > again:
    > if (*task) {
    > curr_task = *task;
    > - curr_files = *fstruct;
    > curr_fd = info->fd;
    > } else {
    > curr_task = task_seq_get_next(ns, &curr_tid, true);
    > if (!curr_task)
    > return NULL;
    >
    > - curr_files = get_files_struct(curr_task);
    > - if (!curr_files) {
    > - put_task_struct(curr_task);
    > - curr_tid = ++(info->tid);
    > - info->fd = 0;
    > - goto again;
    > - }
    > -
    > - /* set *fstruct, *task and info->tid */
    > - *fstruct = curr_files;
    > + /* set *task and info->tid */
    > *task = curr_task;
    > if (curr_tid == info->tid) {
    > curr_fd = info->fd;
    > @@ -179,13 +167,11 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info,
    > }
    >
    > rcu_read_lock();
    > - max_fds = files_fdtable(curr_files)->max_fds;
    > - for (; curr_fd < max_fds; curr_fd++) {
    > + for (;; curr_fd++) {
    > struct file *f;
    > -
    > - f = files_lookup_fd_rcu(curr_files, curr_fd);
    > + f = task_lookup_next_fd_rcu(curr_task, &curr_fd);
    > if (!f)
    > - continue;
    > + break;
    > if (!get_file_rcu(f))
    > continue;
    >
    > @@ -197,10 +183,8 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info,
    >
    > /* the current task is done, go to the next task */
    > rcu_read_unlock();
    > - put_files_struct(curr_files);
    > put_task_struct(curr_task);
    > *task = NULL;
    > - *fstruct = NULL;
    > info->fd = 0;
    > curr_tid = ++(info->tid);
    > goto again;
    > @@ -209,13 +193,11 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info,
    > static void *task_file_seq_start(struct seq_file *seq, loff_t *pos)
    > {
    > struct bpf_iter_seq_task_file_info *info = seq->private;
    > - struct files_struct *files = NULL;
    > struct task_struct *task = NULL;
    > struct file *file;
    >
    > - file = task_file_seq_get_next(info, &task, &files);
    > + file = task_file_seq_get_next(info, &task);
    > if (!file) {
    > - info->files = NULL;
    > info->task = NULL;
    > return NULL;
    > }
    > @@ -223,7 +205,6 @@ static void *task_file_seq_start(struct seq_file *seq, loff_t *pos)
    > if (*pos == 0)
    > ++*pos;
    > info->task = task;
    > - info->files = files;
    >
    > return file;
    > }
    > @@ -231,22 +212,19 @@ static void *task_file_seq_start(struct seq_file *seq, loff_t *pos)
    > static void *task_file_seq_next(struct seq_file *seq, void *v, loff_t *pos)
    > {
    > struct bpf_iter_seq_task_file_info *info = seq->private;
    > - struct files_struct *files = info->files;
    > struct task_struct *task = info->task;
    > struct file *file;
    >
    > ++*pos;
    > ++info->fd;
    > fput((struct file *)v);
    > - file = task_file_seq_get_next(info, &task, &files);
    > + file = task_file_seq_get_next(info, &task);
    > if (!file) {
    > - info->files = NULL;
    > info->task = NULL;
    > return NULL;
    > }
    >
    > info->task = task;
    > - info->files = files;
    >
    > return file;
    > }
    > @@ -295,9 +273,7 @@ static void task_file_seq_stop(struct seq_file *seq, void *v)
    > (void)__task_file_seq_show(seq, v, true);
    > } else {
    > fput((struct file *)v);
    > - put_files_struct(info->files);
    > put_task_struct(info->task);
    > - info->files = NULL;
    > info->task = NULL;
    > }
    > }
    >

    \
     
     \ /
      Last update: 2020-11-23 18:16    [W:3.294 / U:1.156 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site