tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
1
fork

Configure Feed

Select the types of activity you want to include in your feed.

release_task: kill unnecessary rcu_read_lock() around dec_rlimit_ucounts()

rcu_read_lock() was added to shut RCU-lockdep up when this code used
__task_cred()->rcu_dereference(), but after the commit 21d1c5e386bc
("Reimplement RLIMIT_NPROC on top of ucounts") it is no longer needed:
task_ucounts()->task_cred_xxx() takes rcu_read_lock() itself.

NOTE: task_ucounts() returns the pointer to another rcu-protected data,
struct ucounts. So it should either be used when task->real_cred and thus
task->real_cred->ucounts is stable (release_task, copy_process,
copy_creds), or it should be called under rcu_read_lock(). In both cases
it is pointless to take rcu_read_lock() to read the cred->ucounts pointer.

Link: https://lkml.kernel.org/r/20251026143140.GA22463@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Alexey Gladkov <legion@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

authored by

Oleg Nesterov and committed by
Andrew Morton c25d24d0 f9925019

+1 -3
+1 -3
kernel/exit.c
··· 251 251 memset(&post, 0, sizeof(post)); 252 252 253 253 /* don't need to get the RCU readlock here - the process is dead and 254 - * can't be modifying its own credentials. But shut RCU-lockdep up */ 255 - rcu_read_lock(); 254 + * can't be modifying its own credentials. */ 256 255 dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); 257 - rcu_read_unlock(); 258 256 259 257 pidfs_exit(p); 260 258 cgroup_release(p);