Messages in this thread Patch in this message | | | From | Stephen Brennan <> | Subject | [PATCH v6 1/1] proc: Allow pid_revalidate() during LOOKUP_RCU | Date | Mon, 4 Oct 2021 10:56:29 -0700 |
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The pid_revalidate() function drops from RCU into REF lookup mode. When many threads are resolving paths within /proc in parallel, this can result in heavy spinlock contention on d_lockref as each thread tries to grab a reference to the /proc dentry (and drop it shortly thereafter).
Investigation indicates that it is not necessary to drop RCU in pid_revalidate(), as no RCU data is modified and the function never sleeps. So, remove the LOOKUP_RCU check.
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com> --- fs/proc/base.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c index 533d5836eb9a..3042ab418c31 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1979,19 +1979,21 @@ static int pid_revalidate(struct dentry *dentry, unsigned int flags) { struct inode *inode; struct task_struct *task; + int ret = 0; - if (flags & LOOKUP_RCU) - return -ECHILD; - - inode = d_inode(dentry); - task = get_proc_task(inode); + rcu_read_lock(); + inode = d_inode_rcu(dentry); + if (!inode) + goto out; + task = pid_task(proc_pid(inode), PIDTYPE_PID); if (task) { pid_update_inode(task, inode); - put_task_struct(task); - return 1; + ret = 1; } - return 0; +out: + rcu_read_unlock(); + return ret; } static inline bool proc_inode_is_dead(struct inode *inode) -- 2.30.2
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