Messages in this thread | | | Date | Wed, 29 Mar 2023 08:20:57 +0200 | From | Juergen Gross <> | Subject | Re: [PATCH] xen/scsiback: don't call scsiback_free_translation_entry() under lock |
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On 28.03.23 17:47, Oleksandr Tyshchenko wrote: > > > On 28.03.23 11:46, Juergen Gross wrote: > > Hello Juergen > >> scsiback_free_translation_entry() shouldn't be called under spinlock, >> as it can sleep. >> >> This requires to split removing a translation entry from the v2p list >> from actually calling kref_put() for the entry. >> >> Reported-by: Dan Carpenter <error27@gmail.com> >> Link: https://urldefense.com/v3/__https://lore.kernel.org/lkml/Y*JUIl64UDmdkboh@kadam/__;Kw!!GF_29dbcQIUBPA!23IKdVhamoFq8ptUnprd_TubDMObj-0QAalsGiffBHCeEdOuwrq7z4ohg92Sj0olgl0nh73oXvSr-i1zqXhY$ [lore[.]kernel[.]org] >> Signed-off-by: Juergen Gross <jgross@suse.com> >> --- >> drivers/xen/xen-scsiback.c | 27 ++++++++++++++------------- >> 1 file changed, 14 insertions(+), 13 deletions(-) >> >> diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c >> index 954188b0b858..294f29cdc7aa 100644 >> --- a/drivers/xen/xen-scsiback.c >> +++ b/drivers/xen/xen-scsiback.c >> @@ -1010,12 +1010,6 @@ static int scsiback_add_translation_entry(struct vscsibk_info *info, >> return err; >> } >> >> -static void __scsiback_del_translation_entry(struct v2p_entry *entry) >> -{ >> - list_del(&entry->l); >> - kref_put(&entry->kref, scsiback_free_translation_entry); >> -} >> - >> /* >> Delete the translation entry specified >> */ >> @@ -1024,18 +1018,20 @@ static int scsiback_del_translation_entry(struct vscsibk_info *info, >> { >> struct v2p_entry *entry; >> unsigned long flags; >> - int ret = 0; >> >> spin_lock_irqsave(&info->v2p_lock, flags); >> /* Find out the translation entry specified */ >> entry = scsiback_chk_translation_entry(info, v); >> if (entry) >> - __scsiback_del_translation_entry(entry); >> - else >> - ret = -ENOENT; >> + list_del(&entry->l); >> >> spin_unlock_irqrestore(&info->v2p_lock, flags); >> - return ret; >> + >> + if (!entry) >> + return -ENOENT; >> + >> + kref_put(&entry->kref, scsiback_free_translation_entry); >> + return 0; >> } >> >> static void scsiback_do_add_lun(struct vscsibk_info *info, const char *state, >> @@ -1239,14 +1235,19 @@ static void scsiback_release_translation_entry(struct vscsibk_info *info) >> { >> struct v2p_entry *entry, *tmp; >> struct list_head *head = &(info->v2p_entry_lists); >> + struct list_head tmp_list; > > > I would use LIST_HEAD(tmp_list);
There is no need to initialize it, so I think I will keep it as is.
> >> unsigned long flags; >> >> spin_lock_irqsave(&info->v2p_lock, flags); >> >> - list_for_each_entry_safe(entry, tmp, head, l) >> - __scsiback_del_translation_entry(entry); >> + list_cut_before(&tmp_list, head, head); > > so we just move all entries from head to tmp_list here to be processed...
Correct.
> >> >> spin_unlock_irqrestore(&info->v2p_lock, flags); > > ... when the lock is not held, ok > > Patch LGTM, but one (maybe stupid) question to clarify. > > Why do we need to use a lock here in the first place? The > scsiback_release_translation_entry() gets called when the driver > instance is about to be removed and *after* the disconnection from > otherend (so no requests are expected), so what else might cause this > list to be accessed concurrently?
Maybe nothing, but I think it is good practice to keep the lock in order to avoid future code changes to cause problems.
Juergen
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