From: John Hubbard <jhubbard@nvidia.com> To: <jglisse@redhat.com>, <linux-mm@kvack.org> Cc: Andrew Morton <akpm@linux-foundation.org>, <linux-kernel@vger.kernel.org>, Ralph Campbell <rcampbell@nvidia.com>, <stable@vger.kernel.org>, Evgeny Baskakov <ebaskakov@nvidia.com>, Mark Hairgrove <mhairgrove@nvidia.com> Subject: Re: [PATCH 03/14] mm/hmm: HMM should have a callback before MM is destroyed v2 Date: Fri, 16 Mar 2018 20:47:58 -0700 [thread overview] Message-ID: <b0cd570b-dfe4-4b42-18bb-967d1dbddcb3@nvidia.com> (raw) In-Reply-To: <7e87c1f9-5c1a-84fd-1f7f-55ffaaed8a66@nvidia.com> On 03/16/2018 07:36 PM, John Hubbard wrote: > On 03/16/2018 12:14 PM, jglisse@redhat.com wrote: >> From: Ralph Campbell <rcampbell@nvidia.com> >> > > <snip> > >> +static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm) >> +{ >> + struct hmm *hmm = mm->hmm; >> + struct hmm_mirror *mirror; >> + struct hmm_mirror *mirror_next; >> + >> + down_write(&hmm->mirrors_sem); >> + list_for_each_entry_safe(mirror, mirror_next, &hmm->mirrors, list) { >> + list_del_init(&mirror->list); >> + if (mirror->ops->release) >> + mirror->ops->release(mirror); >> + } >> + up_write(&hmm->mirrors_sem); >> +} >> + > > OK, as for actual code review: > > This part of the locking looks good. However, I think it can race against > hmm_mirror_register(), because hmm_mirror_register() will just add a new > mirror regardless. > > So: > > thread 1 thread 2 > -------------- ----------------- > hmm_release hmm_mirror_register > down_write(&hmm->mirrors_sem); <blocked: waiting for sem> > // deletes all list items > up_write > unblocked: adds new mirror > > > ...so I think we need a way to back out of any pending hmm_mirror_register() > calls, as part of the .release steps, right? It seems hard for the device driver, > which could be inside of hmm_mirror_register(), to handle that. Especially considering > that right now, hmm_mirror_register() will return success in this case--so > there is no indication that anything is wrong. > > Maybe hmm_mirror_register() could return an error (and not add to the mirror list), > in such a situation, how's that sound? > In other words, I think this would help (not tested yet beyond a quick compile, but it's pretty simple): diff --git a/mm/hmm.c b/mm/hmm.c index 7ccca5478ea1..da39f8522dca 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -66,6 +66,7 @@ struct hmm { struct list_head mirrors; struct mmu_notifier mmu_notifier; struct rw_semaphore mirrors_sem; + bool shutting_down; }; /* @@ -99,6 +100,7 @@ static struct hmm *hmm_register(struct mm_struct *mm) INIT_LIST_HEAD(&hmm->ranges); spin_lock_init(&hmm->lock); hmm->mm = mm; + hmm->shutting_down = false; /* * We should only get here if hold the mmap_sem in write mode ie on @@ -167,6 +169,7 @@ static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm) struct hmm_mirror *mirror_next; down_write(&hmm->mirrors_sem); + hmm->shutting_down = true; list_for_each_entry_safe(mirror, mirror_next, &hmm->mirrors, list) { list_del_init(&mirror->list); if (mirror->ops->release) @@ -227,6 +230,10 @@ int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm) return -ENOMEM; down_write(&mirror->hmm->mirrors_sem); + if (mirror->hmm->shutting_down) { + up_write(&mirror->hmm->mirrors_sem); + return -ESRCH; + } list_add(&mirror->list, &mirror->hmm->mirrors); up_write(&mirror->hmm->mirrors_sem); thanks, -- John Hubbard NVIDIA
WARNING: multiple messages have this Message-ID (diff)
From: John Hubbard <jhubbard@nvidia.com> To: jglisse@redhat.com, linux-mm@kvack.org Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, Ralph Campbell <rcampbell@nvidia.com>, stable@vger.kernel.org, Evgeny Baskakov <ebaskakov@nvidia.com>, Mark Hairgrove <mhairgrove@nvidia.com> Subject: Re: [PATCH 03/14] mm/hmm: HMM should have a callback before MM is destroyed v2 Date: Fri, 16 Mar 2018 20:47:58 -0700 [thread overview] Message-ID: <b0cd570b-dfe4-4b42-18bb-967d1dbddcb3@nvidia.com> (raw) In-Reply-To: <7e87c1f9-5c1a-84fd-1f7f-55ffaaed8a66@nvidia.com> On 03/16/2018 07:36 PM, John Hubbard wrote: > On 03/16/2018 12:14 PM, jglisse@redhat.com wrote: >> From: Ralph Campbell <rcampbell@nvidia.com> >> > > <snip> > >> +static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm) >> +{ >> + struct hmm *hmm = mm->hmm; >> + struct hmm_mirror *mirror; >> + struct hmm_mirror *mirror_next; >> + >> + down_write(&hmm->mirrors_sem); >> + list_for_each_entry_safe(mirror, mirror_next, &hmm->mirrors, list) { >> + list_del_init(&mirror->list); >> + if (mirror->ops->release) >> + mirror->ops->release(mirror); >> + } >> + up_write(&hmm->mirrors_sem); >> +} >> + > > OK, as for actual code review: > > This part of the locking looks good. However, I think it can race against > hmm_mirror_register(), because hmm_mirror_register() will just add a new > mirror regardless. > > So: > > thread 1 thread 2 > -------------- ----------------- > hmm_release hmm_mirror_register > down_write(&hmm->mirrors_sem); <blocked: waiting for sem> > // deletes all list items > up_write > unblocked: adds new mirror > > > ...so I think we need a way to back out of any pending hmm_mirror_register() > calls, as part of the .release steps, right? It seems hard for the device driver, > which could be inside of hmm_mirror_register(), to handle that. Especially considering > that right now, hmm_mirror_register() will return success in this case--so > there is no indication that anything is wrong. > > Maybe hmm_mirror_register() could return an error (and not add to the mirror list), > in such a situation, how's that sound? > In other words, I think this would help (not tested yet beyond a quick compile, but it's pretty simple): diff --git a/mm/hmm.c b/mm/hmm.c index 7ccca5478ea1..da39f8522dca 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -66,6 +66,7 @@ struct hmm { struct list_head mirrors; struct mmu_notifier mmu_notifier; struct rw_semaphore mirrors_sem; + bool shutting_down; }; /* @@ -99,6 +100,7 @@ static struct hmm *hmm_register(struct mm_struct *mm) INIT_LIST_HEAD(&hmm->ranges); spin_lock_init(&hmm->lock); hmm->mm = mm; + hmm->shutting_down = false; /* * We should only get here if hold the mmap_sem in write mode ie on @@ -167,6 +169,7 @@ static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm) struct hmm_mirror *mirror_next; down_write(&hmm->mirrors_sem); + hmm->shutting_down = true; list_for_each_entry_safe(mirror, mirror_next, &hmm->mirrors, list) { list_del_init(&mirror->list); if (mirror->ops->release) @@ -227,6 +230,10 @@ int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm) return -ENOMEM; down_write(&mirror->hmm->mirrors_sem); + if (mirror->hmm->shutting_down) { + up_write(&mirror->hmm->mirrors_sem); + return -ESRCH; + } list_add(&mirror->list, &mirror->hmm->mirrors); up_write(&mirror->hmm->mirrors_sem); thanks, -- John Hubbard NVIDIA
next prev parent reply other threads:[~2018-03-17 3:48 UTC|newest] Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-03-16 19:14 [PATCH 0/4] hmm: fixes and documentations v2 jglisse 2018-03-16 19:14 ` jglisse 2018-03-16 19:14 ` [PATCH 01/14] mm/hmm: documentation editorial update to HMM documentation jglisse 2018-03-16 19:14 ` jglisse 2018-03-16 19:14 ` [PATCH 02/14] mm/hmm: fix header file if/else/endif maze jglisse 2018-03-16 19:14 ` jglisse 2018-03-16 21:09 ` Andrew Morton 2018-03-16 21:18 ` Jerome Glisse 2018-03-16 21:18 ` Jerome Glisse 2018-03-16 21:18 ` Jerome Glisse 2018-03-16 21:35 ` Andrew Morton 2018-03-16 21:40 ` John Hubbard 2018-03-16 21:40 ` John Hubbard 2018-03-17 1:20 ` [PATCH 02/14] mm/hmm: fix header file if/else/endif maze v2 jglisse 2018-03-17 1:20 ` jglisse 2018-03-16 19:14 ` [PATCH 03/14] mm/hmm: HMM should have a callback before MM is destroyed v2 jglisse 2018-03-16 19:14 ` jglisse 2018-03-16 21:12 ` Andrew Morton 2018-03-16 21:26 ` Jerome Glisse 2018-03-16 21:26 ` Jerome Glisse 2018-03-16 21:26 ` Jerome Glisse 2018-03-16 21:37 ` John Hubbard 2018-03-16 21:37 ` John Hubbard 2018-03-17 2:36 ` John Hubbard 2018-03-17 2:36 ` John Hubbard 2018-03-17 3:47 ` John Hubbard [this message] 2018-03-17 3:47 ` John Hubbard 2018-03-17 4:39 ` John Hubbard 2018-03-17 4:39 ` John Hubbard 2018-03-16 19:14 ` [PATCH 04/14] mm/hmm: hmm_pfns_bad() was accessing wrong struct jglisse 2018-03-16 19:14 ` jglisse 2018-03-17 2:04 ` John Hubbard 2018-03-17 2:04 ` John Hubbard 2018-03-16 19:14 ` [PATCH 05/14] mm/hmm: use struct for hmm_vma_fault(), hmm_vma_get_pfns() parameters jglisse 2018-03-16 19:14 ` jglisse 2018-03-17 3:08 ` John Hubbard 2018-03-17 3:08 ` John Hubbard 2018-03-16 19:14 ` [PATCH 06/14] mm/hmm: remove HMM_PFN_READ flag and ignore peculiar architecture jglisse 2018-03-16 19:14 ` jglisse 2018-03-17 3:30 ` John Hubbard 2018-03-17 3:30 ` John Hubbard 2018-03-16 19:14 ` [PATCH 07/14] mm/hmm: use uint64_t for HMM pfn instead of defining hmm_pfn_t to ulong jglisse 2018-03-16 19:14 ` jglisse 2018-03-17 3:59 ` John Hubbard 2018-03-17 3:59 ` John Hubbard 2018-03-16 19:14 ` [PATCH 08/14] mm/hmm: cleanup special vma handling (VM_SPECIAL) jglisse 2018-03-16 19:14 ` jglisse 2018-03-17 4:35 ` John Hubbard 2018-03-17 4:35 ` John Hubbard 2018-03-16 19:14 ` [PATCH 09/14] mm/hmm: do not differentiate between empty entry or missing directory jglisse 2018-03-16 19:14 ` jglisse 2018-03-19 23:06 ` John Hubbard 2018-03-19 23:06 ` John Hubbard 2018-03-20 2:08 ` Jerome Glisse 2018-03-20 2:08 ` Jerome Glisse
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