From 87c3a86e1c220121d0ced59d1a71e78ed9abc6dd Mon Sep 17 00:00:00 2001 From: Davide Libenzi Date: Wed, 18 Mar 2009 17:04:19 -0700 Subject: [PATCH] eventfd: remove fput() call from possible IRQ context Remove a source of fput() call from inside IRQ context. Myself, like Eric, wasn't able to reproduce an fput() call from IRQ context, but Jeff said he was able to, with the attached test program. Independently from this, the bug is conceptually there, so we might be better off fixing it. This patch adds an optimization similar to the one we already do on ->ki_filp, on ->ki_eventfd. Playing with ->f_count directly is not pretty in general, but the alternative here would be to add a brand new delayed fput() infrastructure, that I'm not sure is worth it. Signed-off-by: Davide Libenzi Cc: Benjamin LaHaise Cc: Trond Myklebust Cc: Eric Dumazet Signed-off-by: Jeff Moyer Cc: Zach Brown Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/aio.c | 37 +++++++++++++++++++++++++++---------- 1 file changed, 27 insertions(+), 10 deletions(-) diff --git a/fs/aio.c b/fs/aio.c index 8fa77e23394..4a9d4d641fb 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -443,7 +443,7 @@ static struct kiocb *__aio_get_req(struct kioctx *ctx) req->private = NULL; req->ki_iovec = NULL; INIT_LIST_HEAD(&req->ki_run_list); - req->ki_eventfd = ERR_PTR(-EINVAL); + req->ki_eventfd = NULL; /* Check if the completion queue has enough free space to * accept an event from this io. @@ -485,8 +485,6 @@ static inline void really_put_req(struct kioctx *ctx, struct kiocb *req) { assert_spin_locked(&ctx->ctx_lock); - if (!IS_ERR(req->ki_eventfd)) - fput(req->ki_eventfd); if (req->ki_dtor) req->ki_dtor(req); if (req->ki_iovec != &req->ki_inline_vec) @@ -508,8 +506,11 @@ static void aio_fput_routine(struct work_struct *data) list_del(&req->ki_list); spin_unlock_irq(&fput_lock); - /* Complete the fput */ - __fput(req->ki_filp); + /* Complete the fput(s) */ + if (req->ki_filp != NULL) + __fput(req->ki_filp); + if (req->ki_eventfd != NULL) + __fput(req->ki_eventfd); /* Link the iocb into the context's free list */ spin_lock_irq(&ctx->ctx_lock); @@ -527,12 +528,14 @@ static void aio_fput_routine(struct work_struct *data) */ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req) { + int schedule_putreq = 0; + dprintk(KERN_DEBUG "aio_put(%p): f_count=%ld\n", req, atomic_long_read(&req->ki_filp->f_count)); assert_spin_locked(&ctx->ctx_lock); - req->ki_users --; + req->ki_users--; BUG_ON(req->ki_users < 0); if (likely(req->ki_users)) return 0; @@ -540,10 +543,23 @@ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req) req->ki_cancel = NULL; req->ki_retry = NULL; - /* Must be done under the lock to serialise against cancellation. - * Call this aio_fput as it duplicates fput via the fput_work. + /* + * Try to optimize the aio and eventfd file* puts, by avoiding to + * schedule work in case it is not __fput() time. In normal cases, + * we would not be holding the last reference to the file*, so + * this function will be executed w/out any aio kthread wakeup. */ - if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count))) { + if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count))) + schedule_putreq++; + else + req->ki_filp = NULL; + if (req->ki_eventfd != NULL) { + if (unlikely(atomic_long_dec_and_test(&req->ki_eventfd->f_count))) + schedule_putreq++; + else + req->ki_eventfd = NULL; + } + if (unlikely(schedule_putreq)) { get_ioctx(ctx); spin_lock(&fput_lock); list_add(&req->ki_list, &fput_head); @@ -1009,7 +1025,7 @@ int aio_complete(struct kiocb *iocb, long res, long res2) * eventfd. The eventfd_signal() function is safe to be called * from IRQ context. */ - if (!IS_ERR(iocb->ki_eventfd)) + if (iocb->ki_eventfd != NULL) eventfd_signal(iocb->ki_eventfd, 1); put_rq: @@ -1608,6 +1624,7 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb, req->ki_eventfd = eventfd_fget((int) iocb->aio_resfd); if (IS_ERR(req->ki_eventfd)) { ret = PTR_ERR(req->ki_eventfd); + req->ki_eventfd = NULL; goto out_put_req; } }