On Fri, Oct 19, 2012 at 10:12 AM, Robert P. J. Day <rpjday@xxxxxxxxxxxxxx> wrote: > > working my way through work queues and read this in workqueue.h: > > /** > * flush_scheduled_work - ensure that any scheduled work has run to completion. > * > * Forces execution of the kernel-global workqueue and blocks until its > * completion. > * > * Think twice before calling this function! It's very easy to get into > * trouble if you don't take great care. Either of the following situations > * will lead to deadlock: > * > * One of the work items currently on the workqueue needs to acquire > * a lock held by your code or its caller. > * > * Your code is running in the context of a work routine. > * > * They will be detected by lockdep when they occur, but the first might not > * occur very often. It depends on what work items are on the workqueue and > * what locks they need, which you have no control over. > * > * In most situations flushing the entire workqueue is overkill; you merely > * need to know that a particular work item isn't queued and isn't running. > * In such cases you should use cancel_delayed_work_sync() or > * cancel_work_sync() instead. > */ > > and yet, there are quite a few drivers that do just that: > > $ grep -rw flush_scheduled_work drivers > drivers/scsi/scsi_scan.c: flush_scheduled_work(); > drivers/scsi/qla2xxx/qla_target.c: flush_scheduled_work(); > drivers/leds/leds-blinkm.c: flush_scheduled_work(); > drivers/acpi/osl.c: * which invoke flush_scheduled_work/acpi_os_wait_events_complete > drivers/staging/olpc_dcon/olpc_dcon.c: flush_scheduled_work(); > drivers/staging/rtl8192u/r8192U_core.c:// flush_scheduled_work(); > drivers/staging/wlan-ng/prism2usb.c: flush_scheduled_work(); > drivers/staging/iio/light/tsl2563.c: flush_scheduled_work(); > drivers/staging/iio/light/tsl2563.c: flush_scheduled_work(); > drivers/staging/rtl8712/usb_intf.c: flush_scheduled_work(); > drivers/message/fusion/mptscsih.c: flush_scheduled_work(); > drivers/rtc/rtc-dev.c: flush_scheduled_work(); > drivers/rtc/rtc-88pm860x.c: flush_scheduled_work(); > drivers/misc/mei/main.c: flush_scheduled_work(); > drivers/misc/mei/main.c: flush_scheduled_work(); > ... snip, even more after this ... > > so what's up with that? it seems inconsistent to describe that > kernel-wide routine as "overkill" while a number of drivers continue > to use it. > > rday Robert, I saw a thread about disk i/o that may relate. At least with disk buffers in the block layer, it appeared it was an all or nothing situation for flushing the queues. So if a upper level wanted to ensure write A completed prior to write B, the only option was: - write A (places data in the block queue) - flush buffers and write all data in the block queue regardless of source - write B (places data in the block queue) I gathered that several of the people in the thread were surprised at the lack of granularity, but no better solution was offered, nor even proposed for the future. Thus, I "assume" the calls you see in the block i/o stack are truly needed. Greg _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
