On Fri, Jul 19, 2024 at 9:27 AM Tom Talpey <tom@xxxxxxxxxx> wrote: > > On 7/19/2024 10:09 AM, David Howells wrote: > > When a subrequest is marked for needing retry, netfs will call > > cifs_prepare_write() which will make cifs repick the server for the op > > before renegotiating credits; it then calls cifs_issue_write() which > > invokes smb2_async_writev() - which re-repicks the server. > > > > If a different server is then selected, this causes the increment of > > server->in_flight to happen against one record and the decrement to happen > > against another, leading to misaccounting. > > > > Fix this by just removing the repick code in smb2_async_writev(). As this > > is only called from netfslib-driven code, cifs_prepare_write() should > > always have been called first, and so server should never be NULL and the > > preparatory step is repeated in the event that we do a retry. > > > > The problem manifests as a warning looking something like: > > > > WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs] > > ... > > RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs] > > ... > > smb2_writev_callback+0x334/0x560 [cifs] > > cifs_demultiplex_thread+0x77a/0x11b0 [cifs] > > kthread+0x187/0x1d0 > > ret_from_fork+0x34/0x60 > > ret_from_fork_asm+0x1a/0x30 > > > > Which may be triggered by a number of different xfstests running against an > > Azure server in multichannel mode. generic/249 seems the most repeatable, > > but generic/215, generic/249 and generic/308 may also show it. > > Nice fix, and good explanation. So, is this the negative-credits issue > we've been looking to fix? Or just one instance? Yes it fixes the only recent crediting issues that I had been seeing. > Feel free to add... > > Acked-by: Tom Talpey <tom@xxxxxxxxxx> Done
