On Mon, Jan 13, 2014 at 11:27 AM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 13 Jan 2014 11:08:58 +0800 Weijie Yang <weijie.yang.kh@xxxxxxxxx> wrote: > >> >> --- a/mm/swapfile.c >> >> +++ b/mm/swapfile.c >> >> @@ -1922,7 +1922,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) >> >> p->swap_map = NULL; >> >> cluster_info = p->cluster_info; >> >> p->cluster_info = NULL; >> >> - p->flags = 0; >> >> frontswap_map = frontswap_map_get(p); >> >> spin_unlock(&p->lock); >> >> spin_unlock(&swap_lock); >> >> @@ -1948,6 +1947,16 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) >> >> mutex_unlock(&inode->i_mutex); >> >> } >> >> filp_close(swap_file, NULL); >> >> + >> >> + /* >> >> + * clear SWP_USED flag after all resources freed >> >> + * so that swapon can reuse this swap_info in alloc_swap_info() safely >> >> + * it is ok to not hold p->lock after we cleared its SWP_WRITEOK >> >> + */ >> >> + spin_lock(&swap_lock); >> >> + p->flags = 0; >> >> + spin_unlock(&swap_lock); >> >> + >> >> err = 0; >> >> atomic_inc(&proc_poll_event); >> >> wake_up_interruptible(&proc_poll_wait); >> > >> > I didn't look too closely, but this patch might also address the race >> > which Krzysztof addressed with >> > http://ozlabs.org/~akpm/mmots/broken-out/swap-fix-setting-page_size-blocksize-during-swapoff-swapon-race.patch. >> > Can we please check that out? >> > >> > I do prefer fixing all these swapon-vs-swapoff races with some large, >> > simple, wide-scope exclusion scheme. Perhaps SWP_USED is that scheme. >> > >> > An alternative would be to add another mutex and just make sys_swapon() >> > and sys_swapoff() 100% exclusive. But that is plastering yet another >> > lock over this mess to hide the horrors which lurk within :( >> > >> >> Hi, Andrew. Thanks for your suggestion. >> >> I checked Krzysztof's patch, it use the global swapon_mutex to protect >> race condition among >> swapon, swapoff and swap_start(). It is a kind of correct method, but >> a heavy method. > > But do you agree that your > http://ozlabs.org/~akpm/mmots/broken-out/mm-swap-fix-race-on-swap_info-reuse-between-swapoff-and-swapon.patch > makes Krzysztof's > http://ozlabs.org/~akpm/mmots/broken-out/swap-fix-setting-page_size-blocksize-during-swapoff-swapon-race.patch > obsolete? Yes, I agree. > I've been sitting on Krzysztof's > swap-fix-setting-page_size-blocksize-during-swapoff-swapon-race.patch > for several months - Hugh had issues with it so I put it on hold and > nothing further happened. > >> I will try to resend a patchset to make lock usage in swapfile.c clear >> and fine grit > > OK, thanks. In the meanwhile I'm planning on dropping Krzysztof's > patch and merging your patch into 3.14-rc1, which is why I'd like > confirmation that your patch addresses the issues which Krzysztof > identified? > I think so, Krzysztof and I both try to fix the same issue(reuse swap_info while its previous resources are not cleared completely). The different is Krzysztof's patch uses a global swapon_mutex and its commit log only focuses on set_blocksize(), while my patch try to maintain the fine grit lock usage. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html