Messages in this thread | | | From | Rik van Riel <> | Subject | [PATCH 0/2] fix rate limited ipc_namespace freeing | Date | Fri, 18 Feb 2022 13:31:12 -0500 |
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The test case below fails on 5.17 (and a bunch of older kernels) with unshare getting -ENOSPC, because the rate at which ipc_namespace structures can be freed is limited by each item on the to-free list waiting in synchronize_rcu.
Making kern_unmount use queue_rcu_work gets rid of that slowdown, allowing a batch of vfsmount structures to be freed after each RCU grace period has expired.
That, in turn, allows us to just get rid of the workqueue in ipc/namespace.c completely.
With these two changes the test case reliably succeeds at calling unshare a million times, even with max_ipc_namespaces reduced to 1000 :)
#define _GNU_SOURCE #include <sched.h> #include <error.h> #include <errno.h> #include <stdlib.h>
int main() { int i;
for (i = 0; i < 1000000; i++) { if (unshare(CLONE_NEWIPC) < 0) error(EXIT_FAILURE, errno, "unshare"); } }
Rik van Riel (2): vfs: free vfsmount through rcu work from kern_unmount ipc: get rid of free_ipc_work workqueue
fs/namespace.c | 11 +++++++++-- include/linux/ipc_namespace.h | 2 -- include/linux/mount.h | 2 ++ ipc/namespace.c | 21 +-------------------- 4 files changed, 12 insertions(+), 24 deletions(-)
-- 2.34.1
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