Messages in this thread |  | | Date | Sat, 28 Nov 2020 20:01:06 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH] proc: add locking checks in proc_inode_is_dead |
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On 11/29, Wen Yang wrote: > > The proc_inode_is_dead function might race with __unhash_process. > This will result in a whole bunch of stale proc entries being cached. > To prevent that, add the required locking.
I leave this to Eric but I don't understand how can this patch help, __unhash_process() can be called right after proc_inode_is_dead().
And in any case, we certainly do not want to take tasklist_lock in proc_inode_is_dead().
> > Signed-off-by: Wen Yang <wenyang@linux.alibaba.com> > Cc: Oleg Nesterov <oleg@redhat.com> > Cc: "Eric W. Biederman" <ebiederm@xmission.com> > Cc: Alexey Dobriyan <adobriyan@gmail.com> > Cc: Christian Brauner <christian@brauner.io> > Cc: linux-kernel@vger.kernel.org > Cc: linux-fsdevel@vger.kernel.org > --- > fs/proc/base.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index 1bc9bcd..59720bc 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -1994,7 +1994,13 @@ static int pid_revalidate(struct dentry *dentry, unsigned int flags) > > static inline bool proc_inode_is_dead(struct inode *inode) > { > - return !proc_pid(inode)->tasks[PIDTYPE_PID].first; > + bool has_task; > + > + read_lock(&tasklist_lock); > + has_task = pid_has_task(proc_pid(inode), PIDTYPE_PID); > + read_unlock(&tasklist_lock); > + > + return !has_task; > } > > int pid_delete_dentry(const struct dentry *dentry) > -- > 1.8.3.1 >
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