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authorThomas Gleixner <tglx@linutronix.de>2021-07-29 13:01:59 +0200
committerThomas Gleixner <tglx@linutronix.de>2021-08-28 01:33:02 +0200
commitb542e383d8c005f06a131e2b40d5889b812f19c6 (patch)
tree14a6c55f5366f44df978f27c4b8a92f0a30b0689 /fs/aio.c
parentsched/fair: Mark tg_is_idle() an inline in the !CONFIG_FAIR_GROUP_SCHED case (diff)
downloadlinux-b542e383d8c005f06a131e2b40d5889b812f19c6.tar.xz
linux-b542e383d8c005f06a131e2b40d5889b812f19c6.zip
eventfd: Make signal recursion protection a task bit
The recursion protection for eventfd_signal() is based on a per CPU variable and relies on the !RT semantics of spin_lock_irqsave() for protecting this per CPU variable. On RT kernels spin_lock_irqsave() neither disables preemption nor interrupts which allows the spin lock held section to be preempted. If the preempting task invokes eventfd_signal() as well, then the recursion warning triggers. Paolo suggested to protect the per CPU variable with a local lock, but that's heavyweight and actually not necessary. The goal of this protection is to prevent the task stack from overflowing, which can be achieved with a per task recursion protection as well. Replace the per CPU variable with a per task bit similar to other recursion protection bits like task_struct::in_page_owner. This works on both !RT and RT kernels and removes as a side effect the extra per CPU storage. No functional change for !RT kernels. Reported-by: Daniel Bristot de Oliveira <bristot@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Daniel Bristot de Oliveira <bristot@redhat.com> Acked-by: Jason Wang <jasowang@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Link: https://lore.kernel.org/r/87wnp9idso.ffs@tglx
Diffstat (limited to 'fs/aio.c')
-rw-r--r--fs/aio.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/aio.c b/fs/aio.c
index 76ce0cc3ee4e..51b08ab01dff 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1695,7 +1695,7 @@ static int aio_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
list_del(&iocb->ki_list);
iocb->ki_res.res = mangle_poll(mask);
req->done = true;
- if (iocb->ki_eventfd && eventfd_signal_count()) {
+ if (iocb->ki_eventfd && eventfd_signal_allowed()) {
iocb = NULL;
INIT_WORK(&req->work, aio_poll_put_work);
schedule_work(&req->work);