Messages in this thread |  | | | Date | Fri, 26 Jun 2009 04:19:31 +0200 | | From | Eric Dumazet <> | | Subject | Re: [PATCH] net: fix race in the receive/select |
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Davide Libenzi a écrit : > On Fri, 26 Jun 2009, Eric Dumazet wrote: > >> Davide Libenzi a écrit : >>> On Thu, 25 Jun 2009, Oleg Nesterov wrote: >>> >>>> Can't really comment this patch, except this all looks reasonable to me. >>>> Add more CCs. >>> While this can work, IMO it'd be cleaner to have the smp_mb() moved from >>> fs/select.c to the ->poll() function. >>> Having a barrier that matches another one in another susbsystem, because >>> of the special locking logic of such subsystem, is not too shiny IMHO. >>> >> Yes but barrier is necessary only if add_wait_queue() was actually called, and __pollwait() >> does this call. >> >> Adding a plain smp_mb() in tcp_poll() for example would slowdown select()/poll() with NULL >> timeout. > > Do you think of it as good design adding an MB on a subsystem, because of > the special locking logic of another one? > The (eventual) slowdown, IMO can be argued sideways, by saying that > non-socket users will pay the price for their polls. >
I wont argue with you David, just try to correct bugs.
fs/ext4/ioctl.c line 182
set_current_state(TASK_INTERRUPTIBLE); add_wait_queue(&EXT4_SB(sb)->ro_wait_queue, &wait); if (timer_pending(&EXT4_SB(sb)->turn_ro_timer)) { schedule(); Another example of missing barrier after add_wait_queue()
Because add_wait_queue() misses a barrier, we have to add one after each call.
Maybe it would be safer to add barrier in add_wait_queue() itself, not in _pollwait().
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