Re: [PATCH v3] efivars,efi-pstore: Hold off deletion of sysfs entry until, the scan is completed

From: Madper Xie
Date: Thu Oct 17 2013 - 11:07:29 EST

Hi folks,
I tested it on my DELL XPS desktop. And it won't show any warnings
when I mounting pstore and deleting pstore items after this patch
applied.

Tested-by: Madper Xie
cxie@xxxxxxxxxx writes:

> Oops, It seems my mu4e(a email client for emacs)'s auto-indent breaks the
> patch... I apologize for this...
>
> seiji.aguchi@xxxxxxx writes:
>
>> Hi Madper,
>>
>> I tested this patch on 3.12-rc4.
>> Could you please send me the log when you failed to apply?
>>
>> Seiji
>>
>>> -----Original Message-----
>>> From: Madper Xie [mailto:cxie@xxxxxxxxxx]
>>> Sent: Thursday, October 17, 2013 1:54 AM
>>> To: Seiji Aguchi
>>> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-efi@xxxxxxxxxxxxxxx; matt.fleming@xxxxxxxxx; tony.luck@xxxxxxxxx; Tomoki Sekiyama; dle-
>>> develop@xxxxxxxxxxxxxxxxxxxxx
>>> Subject: Re: [PATCH v3] efivars,efi-pstore: Hold off deletion of sysfs entry until, the scan is completed
>>>
>>> Howdy Seiji,
>>> I failed appily this patch to both 3.12-rc2 and 3.12-rc4. Could you
>>> please let me know which is the right tree for this patch?
>>>
>>> Thanks,
>>> Madper.
>>> seiji.aguchi@xxxxxxx writes:
>>>
>>> > Change from v2:
>>> > - Move dynamic memory allocation to efi_pstore_read() before holding
>>> > efivars->lock to protect entry->var.Data.
>>> > - Access to entry->scanning while holding efivars->lock.
>>> > - Move a comment about a returned value from efi_pstore_read_func() to
>>> > efi_pstore_read() because "size < 0" case may happen in efi_pstore_read().
>>> >
>>> > Currently, when mounting pstore file system, a read callback of efi_pstore
>>> > driver runs mutiple times as below.
>>> >
>>> > - In the first read callback, scan efivar_sysfs_list from head and pass
>>> > a kmsg buffer of a entry to an upper pstore layer.
>>> > - In the second read callback, rescan efivar_sysfs_list from the entry and pass
>>> > another kmsg buffer to it.
>>> > - Repeat the scan and pass until the end of efivar_sysfs_list.
>>> >
>>> > In this process, an entry is read across the multiple read function calls.
>>> > To avoid race between the read and erasion, the whole process above is
>>> > protected by a spinlock, holding in open() and releasing in close().
>>> >
>>> > At the same time, kmemdup() is called to pass the buffer to pstore filesystem
>>> > during it.
>>> > And then, it causes a following lockdep warning.
>>> >
>>> > To make the dynamic memory allocation runnable without taking spinlock,
>>> > holding off a deletion of sysfs entry if it happens while scanning it
>>> > via efi_pstore, and deleting it after the scan is completed.
>>> >
>>> > To implement it, this patch introduces two flags, scanning and deleting,
>>> > to efivar_entry.
>>> >
>>> > [ 1.143710] ------------[ cut here ]------------
>>> > [ 1.144058] WARNING: CPU: 1 PID: 1 at kernel/lockdep.c:2740
>>> > lockdep_trace_alloc+0x104/0x110()
>>> > [ 1.144058] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
>>> > [ 1.144058] Modules linked in:
>>> >
>>> > [ 1.144058] CPU: 1 PID: 1 Comm: systemd Not tainted 3.11.0-rc5 #2
>>> > [ 1.144058] 0000000000000009 ffff8800797e9ae0 ffffffff816614a5
>>> > ffff8800797e9b28
>>> > [ 1.144058] ffff8800797e9b18 ffffffff8105510d 0000000000000080
>>> > 0000000000000046
>>> > [ 1.144058] 00000000000000d0 00000000000003af ffffffff81ccd0c0
>>> > ffff8800797e9b78
>>> > [ 1.144058] Call Trace:
>>> > [ 1.144058] [<ffffffff816614a5>] dump_stack+0x54/0x74
>>> > [ 1.144058] [<ffffffff8105510d>] warn_slowpath_common+0x7d/0xa0
>>> > [ 1.144058] [<ffffffff8105517c>] warn_slowpath_fmt+0x4c/0x50
>>> > [ 1.144058] [<ffffffff8131290f>] ? vsscanf+0x57f/0x7b0
>>> > [ 1.144058] [<ffffffff810bbd74>] lockdep_trace_alloc+0x104/0x110
>>> > [ 1.144058] [<ffffffff81192da0>] __kmalloc_track_caller+0x50/0x280
>>> > [ 1.144058] [<ffffffff815147bb>] ?
>>> > efi_pstore_read_func.part.1+0x12b/0x170
>>> > [ 1.144058] [<ffffffff8115b260>] kmemdup+0x20/0x50
>>> > [ 1.144058] [<ffffffff815147bb>] efi_pstore_read_func.part.1+0x12b/0x170
>>> > [ 1.144058] [<ffffffff81514800>] ?
>>> > efi_pstore_read_func.part.1+0x170/0x170
>>> > [ 1.144058] [<ffffffff815148b4>] efi_pstore_read_func+0xb4/0xe0
>>> > [ 1.144058] [<ffffffff81512b7b>] __efivar_entry_iter+0xfb/0x120
>>> > [ 1.144058] [<ffffffff8151428f>] efi_pstore_read+0x3f/0x50
>>> > [ 1.144058] [<ffffffff8128d7ba>] pstore_get_records+0x9a/0x150
>>> > [ 1.158207] [<ffffffff812af25c>] ? selinux_d_instantiate+0x1c/0x20
>>> > [ 1.158207] [<ffffffff8128ce30>] ? parse_options+0x80/0x80
>>> > [ 1.158207] [<ffffffff8128ced5>] pstore_fill_super+0xa5/0xc0
>>> > [ 1.158207] [<ffffffff811ae7d2>] mount_single+0xa2/0xd0
>>> > [ 1.158207] [<ffffffff8128ccf8>] pstore_mount+0x18/0x20
>>> > [ 1.158207] [<ffffffff811ae8b9>] mount_fs+0x39/0x1b0
>>> > [ 1.158207] [<ffffffff81160550>] ? __alloc_percpu+0x10/0x20
>>> > [ 1.158207] [<ffffffff811c9493>] vfs_kern_mount+0x63/0xf0
>>> > [ 1.158207] [<ffffffff811cbb0e>] do_mount+0x23e/0xa20
>>> > [ 1.158207] [<ffffffff8115b51b>] ? strndup_user+0x4b/0xf0
>>> > [ 1.158207] [<ffffffff811cc373>] SyS_mount+0x83/0xc0
>>> > [ 1.158207] [<ffffffff81673cc2>] system_call_fastpath+0x16/0x1b
>>> > [ 1.158207] ---[ end trace 61981bc62de9f6f4 ]---
>>> >
>>> > Signed-off-by: Seiji Aguchi <seiji.aguchi@xxxxxxx>
>>> > ---
>>> > drivers/firmware/efi/efi-pstore.c | 143 +++++++++++++++++++++++++++++++++++---
>>> > drivers/firmware/efi/efivars.c | 12 ++--
>>> > drivers/firmware/efi/vars.c | 12 +++-
>>> > include/linux/efi.h | 2 +
>>> > 4 files changed, 153 insertions(+), 16 deletions(-)
>>> >
>>> > diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
>>> > index 5002d50..ebd5dbc 100644
>>> > --- a/drivers/firmware/efi/efi-pstore.c
>>> > +++ b/drivers/firmware/efi/efi-pstore.c
>>> > @@ -18,14 +18,12 @@ module_param_named(pstore_disable, efivars_pstore_disable, bool, 0644);
>>> >
>>> > static int efi_pstore_open(struct pstore_info *psi)
>>> > {
>>> > - efivar_entry_iter_begin();
>>> > psi->data = NULL;
>>> > return 0;
>>> > }
>>> >
>>> > static int efi_pstore_close(struct pstore_info *psi)
>>> > {
>>> > - efivar_entry_iter_end();
>>> > psi->data = NULL;
>>> > return 0;
>>> > }
>>> > @@ -91,19 +89,125 @@ static int efi_pstore_read_func(struct efivar_entry *entry, void *data)
>>> > __efivar_entry_get(entry, &entry->var.Attributes,
>>> > &entry->var.DataSize, entry->var.Data);
>>> > size = entry->var.DataSize;
>>> > + memcpy(*cb_data->buf, entry->var.Data, (size_t)min_t(unsigned long,
>>> > + 1024, size));
>>> >
>>> > - *cb_data->buf = kmemdup(entry->var.Data, size, GFP_KERNEL);
>>> > - if (*cb_data->buf == NULL)
>>> > - return -ENOMEM;
>>> > return size;
>>> > }
>>> >
>>> > +/**
>>> > + * efi_pstore_scan_sysfs_enter
>>> > + * @entry: scanning entry
>>> > + * @next: next entry
>>> > + * @head: list head
>>> > + */
>>> > +static void efi_pstore_scan_sysfs_enter(struct efivar_entry *pos,
>>> > + struct efivar_entry *next,
>>> > + struct list_head *head)
>>> > +{
>>> > + pos->scanning = true;
>>> > + if (&next->list != head)
>>> > + next->scanning = true;
>>> > +}
>>> > +
>>> > +/**
>>> > + * __efi_pstore_scan_sysfs_exit
>>> > + * @entry: deleting entry
>>> > + * @turn_off_scanning: Check if a scanning flag should be turned off
>>> > + */
>>> > +static inline void __efi_pstore_scan_sysfs_exit(struct efivar_entry *entry,
>>> > + bool turn_off_scanning)
>>> > +{
>>> > + if (entry->deleting) {
>>> > + list_del(&entry->list);
>>> > + efivar_entry_iter_end();
>>> > + efivar_unregister(entry);
>>> > + efivar_entry_iter_begin();
>>> > + } else if (turn_off_scanning)
>>> > + entry->scanning = false;
>>> > +}
>>> > +
>>> > +/**
>>> > + * efi_pstore_scan_sysfs_exit
>>> > + * @pos: scanning entry
>>> > + * @next: next entry
>>> > + * @head: list head
>>> > + * @stop: a flag checking if scanning will stop
>>> > + */
>>> > +static void efi_pstore_scan_sysfs_exit(struct efivar_entry *pos,
>>> > + struct efivar_entry *next,
>>> > + struct list_head *head, bool stop)
>>> > +{
>>> > + __efi_pstore_scan_sysfs_exit(pos, true);
>>> > + if (stop)
>>> > + __efi_pstore_scan_sysfs_exit(next, &next->list != head);
>>> > +}
>>> > +
>>> > +/**
>>> > + * efi_pstore_sysfs_entry_iter
>>> > + *
>>> > + * @data: function-specific data to pass to callback
>>> > + * @pos: entry to begin iterating from
>>> > + *
>>> > + * You MUST call efivar_enter_iter_begin() before this function, and
>>> > + * efivar_entry_iter_end() afterwards.
>>> > + *
>>> > + * It is possible to begin iteration from an arbitrary entry within
>>> > + * the list by passing @pos. @pos is updated on return to point to
>>> > + * the next entry of the last one passed to efi_pstore_read_func().
>>> > + * To begin iterating from the beginning of the list @pos must be %NULL.
>>> > + */
>>> > +static int efi_pstore_sysfs_entry_iter(void *data, struct efivar_entry **pos)
>>> > +{
>>> > + struct efivar_entry *entry, *n;
>>> > + struct list_head *head = &efivar_sysfs_list;
>>> > + int size = 0;
>>> > +
>>> > + if (!*pos) {
>>> > + list_for_each_entry_safe(entry, n, head, list) {
>>> > + efi_pstore_scan_sysfs_enter(entry, n, head);
>>> > +
>>> > + size = efi_pstore_read_func(entry, data);
>>> > + efi_pstore_scan_sysfs_exit(entry, n, head, size < 0);
>>> > + if (size)
>>> > + break;
>>> > + }
>>> > + *pos = n;
>>> > + return size;
>>> > + }
>>> > +
>>> > + list_for_each_entry_safe_from((*pos), n, head, list) {
>>> > + efi_pstore_scan_sysfs_enter((*pos), n, head);
>>> > +
>>> > + size = efi_pstore_read_func((*pos), data);
>>> > + efi_pstore_scan_sysfs_exit((*pos), n, head, size < 0);
>>> > + if (size)
>>> > + break;
>>> > + }
>>> > + *pos = n;
>>> > + return size;
>>> > +}
>>> > +
>>> > +/**
>>> > + * efi_pstore_read
>>> > + *
>>> > + * This function returns a size of NVRAM entry logged via efi_pstore_write().
>>> > + * The meaning and behavior of efi_pstore/pstore are as below.
>>> > + *
>>> > + * size > 0: Got data of an entry logged via efi_pstore_write() successfully,
>>> > + * and pstore filesystem will continue reading subsequent entries.
>>> > + * size == 0: Entry was not logged via efi_pstore_write(),
>>> > + * and efi_pstore driver will continue reading subsequent entries.
>>> > + * size < 0: Failed to get data of entry logging via efi_pstore_write(),
>>> > + * and pstore will stop reading entry.
>>> > + */
>>> > static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
>>> > int *count, struct timespec *timespec,
>>> > char **buf, bool *compressed,
>>> > struct pstore_info *psi)
>>> > {
>>> > struct pstore_read_data data;
>>> > + ssize_t size;
>>> >
>>> > data.id = id;
>>> > data.type = type;
>>> > @@ -112,8 +216,17 @@ static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
>>> > data.compressed = compressed;
>>> > data.buf = buf;
>>> >
>>> > - return __efivar_entry_iter(efi_pstore_read_func, &efivar_sysfs_list, &data,
>>> > - (struct efivar_entry **)&psi->data);
>>> > + *data.buf = kzalloc(1024, GFP_KERNEL);
>>> > + if (!*data.buf)
>>> > + return -ENOMEM;
>>> > +
>>> > + efivar_entry_iter_begin();
>>> > + size = efi_pstore_sysfs_entry_iter(&data,
>>> > + (struct efivar_entry **)&psi->data);
>>> > + efivar_entry_iter_end();
>>> > + if (size <= 0)
>>> > + kfree(*data.buf);
>>> > + return size;
>>> > }
>>> >
>>> > static int efi_pstore_write(enum pstore_type_id type,
>>> > @@ -184,9 +297,17 @@ static int efi_pstore_erase_func(struct efivar_entry *entry, void *data)
>>> > return 0;
>>> > }
>>> >
>>> > + if (entry->scanning) {
>>> > + /*
>>> > + * Skip deletion because this entry will be deleted
>>> > + * after scanning is completed.
>>> > + */
>>> > + entry->deleting = true;
>>> > + } else
>>> > + list_del(&entry->list);
>>> > +
>>> > /* found */
>>> > __efivar_entry_delete(entry);
>>> > - list_del(&entry->list);
>>> >
>>> > return 1;
>>> > }
>>> > @@ -214,10 +335,12 @@ static int efi_pstore_erase(enum pstore_type_id type, u64 id, int count,
>>> >
>>> > efivar_entry_iter_begin();
>>> > found = __efivar_entry_iter(efi_pstore_erase_func, &efivar_sysfs_list, &edata, &entry);
>>> > - efivar_entry_iter_end();
>>> >
>>> > - if (found)
>>> > + if (found && !entry->scanning) {
>>> > + efivar_entry_iter_end();
>>> > efivar_unregister(entry);
>>> > + } else
>>> > + efivar_entry_iter_end();
>>> >
>>> > return 0;
>>> > }
>>> > diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c
>>> > index 8a7432a..8c5a61a 100644
>>> > --- a/drivers/firmware/efi/efivars.c
>>> > +++ b/drivers/firmware/efi/efivars.c
>>> > @@ -383,12 +383,16 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
>>> > else if (__efivar_entry_delete(entry))
>>> > err = -EIO;
>>> >
>>> > - efivar_entry_iter_end();
>>> > -
>>> > - if (err)
>>> > + if (err) {
>>> > + efivar_entry_iter_end();
>>> > return err;
>>> > + }
>>> >
>>> > - efivar_unregister(entry);
>>> > + if (!entry->scanning) {
>>> > + efivar_entry_iter_end();
>>> > + efivar_unregister(entry);
>>> > + } else
>>> > + efivar_entry_iter_end();
>>> >
>>> > /* It's dead Jim.... */
>>> > return count;
>>> > diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
>>> > index 391c67b..b22659c 100644
>>> > --- a/drivers/firmware/efi/vars.c
>>> > +++ b/drivers/firmware/efi/vars.c
>>> > @@ -683,8 +683,16 @@ struct efivar_entry *efivar_entry_find(efi_char16_t *name, efi_guid_t guid,
>>> > if (!found)
>>> > return NULL;
>>> >
>>> > - if (remove)
>>> > - list_del(&entry->list);
>>> > + if (remove) {
>>> > + if (entry->scanning) {
>>> > + /*
>>> > + * The entry will be deleted
>>> > + * after scanning is completed.
>>> > + */
>>> > + entry->deleting = true;
>>> > + } else
>>> > + list_del(&entry->list);
>>> > + }
>>> >
>>> > return entry;
>>> > }
>>> > diff --git a/include/linux/efi.h b/include/linux/efi.h
>>> > index 5f8f176..04088fb 100644
>>> > --- a/include/linux/efi.h
>>> > +++ b/include/linux/efi.h
>>> > @@ -782,6 +782,8 @@ struct efivar_entry {
>>> > struct efi_variable var;
>>> > struct list_head list;
>>> > struct kobject kobj;
>>> > + bool scanning;
>>> > + bool deleting;
>>> > };
>>> >
>>> > extern struct list_head efivar_sysfs_list;
>>>
>>>
>>> --
>>> Best,
>>> Madper Xie.


--
Best,
Madper Xie.
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