| Message ID | 1376938.1613429183@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Network fs helper library & fscache kiocb API [ver #3] | expand |
On Mon, Feb 15, 2021 at 10:46:23PM +0000, David Howells wrote: > The in_softirq() in netfs_rreq_terminated() works fine for the cache being > on a normal disk, as the completion handlers may get called in softirq > context, but for an NVMe drive, the completion handler may get called in > IRQ context. > > Fix to use in_interrupt() instead of in_softirq() throughout the read > helpers, particularly when deciding whether to punt code that might sleep > off to a worker thread. We must not use either check, as they all are unreliable especially for PREEMPT-RT.
On 2021-02-16 09:42:30 [+0100], Christoph Hellwig wrote: > On Mon, Feb 15, 2021 at 10:46:23PM +0000, David Howells wrote: > > The in_softirq() in netfs_rreq_terminated() works fine for the cache being > > on a normal disk, as the completion handlers may get called in softirq > > context, but for an NVMe drive, the completion handler may get called in > > IRQ context. > > > > Fix to use in_interrupt() instead of in_softirq() throughout the read > > helpers, particularly when deciding whether to punt code that might sleep > > off to a worker thread. > > We must not use either check, as they all are unreliable especially > for PREEMPT-RT. Yes, please. I try to cleanup the users one by one https://lore.kernel.org/r/20200914204209.256266093@linutronix.de/ https://lore.kernel.org/amd-gfx/20210209124439.408140-1-bigeasy@linutronix.de/ Sebastian
Christoph Hellwig <hch@lst.de> wrote: > On Mon, Feb 15, 2021 at 10:46:23PM +0000, David Howells wrote: > > The in_softirq() in netfs_rreq_terminated() works fine for the cache being > > on a normal disk, as the completion handlers may get called in softirq > > context, but for an NVMe drive, the completion handler may get called in > > IRQ context. > > > > Fix to use in_interrupt() instead of in_softirq() throughout the read > > helpers, particularly when deciding whether to punt code that might sleep > > off to a worker thread. > > We must not use either check, as they all are unreliable especially > for PREEMPT-RT. Is there a better way to do it? The intent is to process the assessment phase in the calling thread's context if possible rather than bumping over to a worker thread. For synchronous I/O, for example, that's done in the caller's thread. Maybe that's the answer - if it's known to be asynchronous, I have to punt, but otherwise don't have to. David
On Tue, Feb 16, 2021 at 09:29:31AM +0000, David Howells wrote: > Is there a better way to do it? The intent is to process the assessment phase > in the calling thread's context if possible rather than bumping over to a > worker thread. For synchronous I/O, for example, that's done in the caller's > thread. Maybe that's the answer - if it's known to be asynchronous, I have to > punt, but otherwise don't have to. Yes, i think you want an explicit flag instead.
diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c index 9191a3617d91..db582008b4bd 100644 --- a/fs/netfs/read_helper.c +++ b/fs/netfs/read_helper.c @@ -96,7 +96,7 @@ static void netfs_free_read_request(struct work_struct *work) static void netfs_put_read_request(struct netfs_read_request *rreq) { if (refcount_dec_and_test(&rreq->usage)) { - if (in_softirq()) { + if (in_interrupt()) { rreq->work.func = netfs_free_read_request; if (!queue_work(system_unbound_wq, &rreq->work)) BUG(); @@ -353,7 +353,7 @@ static void netfs_rreq_write_to_cache_work(struct work_struct *work) static void netfs_rreq_write_to_cache(struct netfs_read_request *rreq) { - if (in_softirq()) { + if (in_interrupt()) { rreq->work.func = netfs_rreq_write_to_cache_work; if (!queue_work(system_unbound_wq, &rreq->work)) BUG(); @@ -479,7 +479,7 @@ static bool netfs_rreq_perform_resubmissions(struct netfs_read_request *rreq) { struct netfs_read_subrequest *subreq; - WARN_ON(in_softirq()); + WARN_ON(in_interrupt()); trace_netfs_rreq(rreq, netfs_rreq_trace_resubmit); @@ -577,7 +577,7 @@ static void netfs_rreq_work(struct work_struct *work) static void netfs_rreq_terminated(struct netfs_read_request *rreq) { if (test_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags) && - in_softirq()) { + in_interrupt()) { if (!queue_work(system_unbound_wq, &rreq->work)) BUG(); } else {
The in_softirq() in netfs_rreq_terminated() works fine for the cache being on a normal disk, as the completion handlers may get called in softirq context, but for an NVMe drive, the completion handler may get called in IRQ context. Fix to use in_interrupt() instead of in_softirq() throughout the read helpers, particularly when deciding whether to punt code that might sleep off to a worker thread. The symptom involves warnings like the following appearing and the kernel hanging: WARNING: CPU: 0 PID: 0 at kernel/softirq.c:175 __local_bh_enable_ip+0x35/0x50 ... RIP: 0010:__local_bh_enable_ip+0x35/0x50 ... Call Trace: <IRQ> rxrpc_kernel_begin_call+0x7d/0x1b0 [rxrpc] ? afs_rx_new_call+0x40/0x40 [kafs] ? afs_alloc_call+0x28/0x120 [kafs] afs_make_call+0x120/0x510 [kafs] ? afs_rx_new_call+0x40/0x40 [kafs] ? afs_alloc_flat_call+0xba/0x100 [kafs] ? __kmalloc+0x167/0x2f0 ? afs_alloc_flat_call+0x9b/0x100 [kafs] afs_wait_for_operation+0x2d/0x200 [kafs] afs_do_sync_operation+0x16/0x20 [kafs] afs_req_issue_op+0x8c/0xb0 [kafs] netfs_rreq_assess+0x125/0x7d0 [netfs] ? cachefiles_end_operation+0x40/0x40 [cachefiles] netfs_subreq_terminated+0x117/0x220 [netfs] cachefiles_read_complete+0x21/0x60 [cachefiles] iomap_dio_bio_end_io+0xdd/0x110 blk_update_request+0x20a/0x380 blk_mq_end_request+0x1c/0x120 nvme_process_cq+0x159/0x1f0 [nvme] nvme_irq+0x10/0x20 [nvme] __handle_irq_event_percpu+0x37/0x150 handle_irq_event+0x49/0xb0 handle_edge_irq+0x7c/0x200 asm_call_irq_on_stack+0xf/0x20 </IRQ> common_interrupt+0xad/0x120 asm_common_interrupt+0x1e/0x40 ... Reported-by: Marc Dionne <marc.dionne@auristor.com> Signed-off-by: David Howells <dhowells@redhat.com> cc: Matthew Wilcox <willy@infradead.org> cc: linux-mm@kvack.org cc: linux-cachefs@redhat.com cc: linux-afs@lists.infradead.org cc: linux-nfs@vger.kernel.org cc: linux-cifs@vger.kernel.org cc: ceph-devel@vger.kernel.org cc: v9fs-developer@lists.sourceforge.net cc: linux-fsdevel@vger.kernel.org --- read_helper.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)