* [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
@ 2019-08-01 9:17 Zhihao Cheng
2019-08-01 9:13 ` 答复: " chengzhihao
0 siblings, 1 reply; 6+ messages in thread
From: Zhihao Cheng @ 2019-08-01 9:17 UTC (permalink / raw)
To: richard, yi.zhang; +Cc: linux-mtd, linux-kernel, chengzhihao1
Running pressure test io_paral (A pressure ubi test in mtd-utils) on an
UBI device with fewer PEBs (fastmap enabled) may cause ENOSPC errors and
make UBI device read-only, but there are still free PEBs on the UBI
device. This problem can be easily reproduced by performing the following
steps on a 2-core machine:
$ modprobe nandsim first_id_byte=0x20 second_id_byte=0x33 parts=80
$ modprobe ubi mtd="0,0" fm_autoconvert
$ ./io_paral /dev/ubi0
We may see the following verbose:
(output)
[io_paral] update_volume():105: function write() failed with error 30
(Read-only file system)
[io_paral] update_volume():108: failed to write 380 bytes at offset
95920 of volume 2
[io_paral] update_volume():109: update: 97088 bytes
[io_paral] write_thread():227: function pwrite() failed with error 28
(No space left on device)
[io_paral] write_thread():229: cannot write 15872 bytes to offs 31744,
wrote -1
(dmesg)
ubi0 error: ubi_wl_get_peb [ubi]: Unable to get a free PEB from user WL
pool
ubi0 warning: ubi_eba_write_leb [ubi]: switch to read-only mode
ubi0 error: ubi_io_write [ubi]: read-only mode
CPU: 0 PID: 2027 Comm: io_paral Not tainted 5.3.0-rc2-00001-g5986cd0 #9
ubi0 warning: try_write_vid_and_data [ubi]: failed to write VID header
to LEB 2:5, PEB 18
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0
-0-ga698c8995f-prebuilt.qemu.org 04/01/2014
Call Trace:
dump_stack+0x85/0xba
ubi_eba_write_leb+0xa1e/0xa40 [ubi]
vol_cdev_write+0x307/0x520 [ubi]
ubi0 error: vol_cdev_write [ubi]: cannot accept more 380 bytes of data,
error -30
vfs_write+0xfa/0x280
ksys_pwrite64+0xc5/0xe0
__x64_sys_pwrite64+0x22/0x30
do_syscall_64+0xbf/0x440
In function ubi_wl_get_peb, the operation of filling the pool
(ubi_update_fastmap) with free PEBs and fetching a free PEB from the pool
is not atomic. After thread A filling the pool with free PEB, free PEB may
be taken away by thread B. When thread A checks the expression again, the
condition is still unsatisfactory. At this time, there may still be free
PEBs on UBI that can be filled into the pool.
So, ubi_wl_get_peb (in fastmap-wil.c) should be implemented to obtain a
free PEB by polling method. The polling exit condition is that there is
no free PEBs on UBI, no free PEBs in pool, and ubi->works_count is 0.
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
---
drivers/mtd/ubi/fastmap-wl.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/mtd/ubi/fastmap-wl.c b/drivers/mtd/ubi/fastmap-wl.c
index d9e2e3a..c5512cf 100644
--- a/drivers/mtd/ubi/fastmap-wl.c
+++ b/drivers/mtd/ubi/fastmap-wl.c
@@ -196,7 +196,7 @@ static int produce_free_peb(struct ubi_device *ubi)
*/
int ubi_wl_get_peb(struct ubi_device *ubi)
{
- int ret, retried = 0;
+ int ret;
struct ubi_fm_pool *pool = &ubi->fm_pool;
struct ubi_fm_pool *wl_pool = &ubi->fm_wl_pool;
@@ -220,13 +220,14 @@ int ubi_wl_get_peb(struct ubi_device *ubi)
}
if (pool->used == pool->size) {
- spin_unlock(&ubi->wl_lock);
- if (retried) {
+ if (!ubi->free.rb_node && ubi->works_count == 0) {
ubi_err(ubi, "Unable to get a free PEB from user WL pool");
+ ubi_assert(list_empty(&ubi->works));
+ spin_unlock(&ubi->wl_lock);
ret = -ENOSPC;
goto out;
}
- retried = 1;
+ spin_unlock(&ubi->wl_lock);
up_read(&ubi->fm_eba_sem);
ret = produce_free_peb(ubi);
if (ret < 0) {
--
2.7.4
^ permalink raw reply related [flat|nested] 6+ messages in thread
* 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
2019-08-01 9:17 [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB Zhihao Cheng
@ 2019-08-01 9:13 ` chengzhihao
2019-08-01 9:20 ` Richard Weinberger
0 siblings, 1 reply; 6+ messages in thread
From: chengzhihao @ 2019-08-01 9:13 UTC (permalink / raw)
To: richard, zhangyi (F); +Cc: linux-mtd, linux-kernel
I don't quite understand why a limited number of attempts have been made to get a free PEB in ubi_wl_get_peb (in fastmap-wl.c). I proposed this PATCH with reference to the implementation of ubi_wl_get_peb (in wl.c). As far as I know, getting PEB by polling probably won't fall into soft-lockup.
ubi_update_fastmap may add new tasks (including erase task or wl taskk, wl tasks generally do not generate additional free PEBs) to ubi->works, and produce_free_peb will eventually complete all tasks in ubi->works or obtain an free PEB that can be filled into pool.
-----邮件原件-----
发件人: chengzhihao
发送时间: 2019年8月1日 17:18
收件人: richard@nod.at; zhangyi (F) <yi.zhang@huawei.com>
抄送: linux-mtd@lists.infradead.org; linux-kernel@vger.kernel.org; chengzhihao <chengzhihao1@huawei.com>
主题: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
Running pressure test io_paral (A pressure ubi test in mtd-utils) on an UBI device with fewer PEBs (fastmap enabled) may cause ENOSPC errors and make UBI device read-only, but there are still free PEBs on the UBI device. This problem can be easily reproduced by performing the following steps on a 2-core machine:
$ modprobe nandsim first_id_byte=0x20 second_id_byte=0x33 parts=80
$ modprobe ubi mtd="0,0" fm_autoconvert
$ ./io_paral /dev/ubi0
We may see the following verbose:
(output)
[io_paral] update_volume():105: function write() failed with error 30
(Read-only file system)
[io_paral] update_volume():108: failed to write 380 bytes at offset
95920 of volume 2
[io_paral] update_volume():109: update: 97088 bytes
[io_paral] write_thread():227: function pwrite() failed with error 28
(No space left on device)
[io_paral] write_thread():229: cannot write 15872 bytes to offs 31744,
wrote -1
(dmesg)
ubi0 error: ubi_wl_get_peb [ubi]: Unable to get a free PEB from user WL
pool
ubi0 warning: ubi_eba_write_leb [ubi]: switch to read-only mode
ubi0 error: ubi_io_write [ubi]: read-only mode
CPU: 0 PID: 2027 Comm: io_paral Not tainted 5.3.0-rc2-00001-g5986cd0 #9
ubi0 warning: try_write_vid_and_data [ubi]: failed to write VID header
to LEB 2:5, PEB 18
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0
-0-ga698c8995f-prebuilt.qemu.org 04/01/2014
Call Trace:
dump_stack+0x85/0xba
ubi_eba_write_leb+0xa1e/0xa40 [ubi]
vol_cdev_write+0x307/0x520 [ubi]
ubi0 error: vol_cdev_write [ubi]: cannot accept more 380 bytes of data,
error -30
vfs_write+0xfa/0x280
ksys_pwrite64+0xc5/0xe0
__x64_sys_pwrite64+0x22/0x30
do_syscall_64+0xbf/0x440
In function ubi_wl_get_peb, the operation of filling the pool
(ubi_update_fastmap) with free PEBs and fetching a free PEB from the pool is not atomic. After thread A filling the pool with free PEB, free PEB may be taken away by thread B. When thread A checks the expression again, the condition is still unsatisfactory. At this time, there may still be free PEBs on UBI that can be filled into the pool.
So, ubi_wl_get_peb (in fastmap-wil.c) should be implemented to obtain a free PEB by polling method. The polling exit condition is that there is no free PEBs on UBI, no free PEBs in pool, and ubi->works_count is 0.
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
---
drivers/mtd/ubi/fastmap-wl.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/mtd/ubi/fastmap-wl.c b/drivers/mtd/ubi/fastmap-wl.c index d9e2e3a..c5512cf 100644
--- a/drivers/mtd/ubi/fastmap-wl.c
+++ b/drivers/mtd/ubi/fastmap-wl.c
@@ -196,7 +196,7 @@ static int produce_free_peb(struct ubi_device *ubi)
*/
int ubi_wl_get_peb(struct ubi_device *ubi) {
- int ret, retried = 0;
+ int ret;
struct ubi_fm_pool *pool = &ubi->fm_pool;
struct ubi_fm_pool *wl_pool = &ubi->fm_wl_pool;
@@ -220,13 +220,14 @@ int ubi_wl_get_peb(struct ubi_device *ubi)
}
if (pool->used == pool->size) {
- spin_unlock(&ubi->wl_lock);
- if (retried) {
+ if (!ubi->free.rb_node && ubi->works_count == 0) {
ubi_err(ubi, "Unable to get a free PEB from user WL pool");
+ ubi_assert(list_empty(&ubi->works));
+ spin_unlock(&ubi->wl_lock);
ret = -ENOSPC;
goto out;
}
- retried = 1;
+ spin_unlock(&ubi->wl_lock);
up_read(&ubi->fm_eba_sem);
ret = produce_free_peb(ubi);
if (ret < 0) {
--
2.7.4
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
2019-08-01 9:13 ` 答复: " chengzhihao
@ 2019-08-01 9:20 ` Richard Weinberger
2019-08-01 9:26 ` 答复: " chengzhihao
0 siblings, 1 reply; 6+ messages in thread
From: Richard Weinberger @ 2019-08-01 9:20 UTC (permalink / raw)
To: chengzhihao1; +Cc: yi zhang, linux-mtd, linux-kernel
----- Ursprüngliche Mail -----
> Von: "chengzhihao1" <chengzhihao1@huawei.com>
> An: "richard" <richard@nod.at>, "yi zhang" <yi.zhang@huawei.com>
> CC: "linux-mtd" <linux-mtd@lists.infradead.org>, "linux-kernel" <linux-kernel@vger.kernel.org>
> Gesendet: Donnerstag, 1. August 2019 11:13:20
> Betreff: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
> I don't quite understand why a limited number of attempts have been made to get
> a free PEB in ubi_wl_get_peb (in fastmap-wl.c). I proposed this PATCH with
> reference to the implementation of ubi_wl_get_peb (in wl.c). As far as I know,
> getting PEB by polling probably won't fall into soft-lockup.
> ubi_update_fastmap may add new tasks (including erase task or wl taskk, wl tasks
> generally do not generate additional free PEBs) to ubi->works, and
> produce_free_peb will eventually complete all tasks in ubi->works or obtain an
> free PEB that can be filled into pool.
You send this patch three times, I guess your mail setup has issues? :-)
This is one of the darkest corners of Fastmap where things get messy.
The number of retry attempts was limited to avoid a live lock.
I agree that allowing only one retry is a little to few.
With nandsim, a small nand and a fast PC you can hit that.
Do you have numbers how many attempts were needed to get a free block?
Thanks,
//richard
^ permalink raw reply [flat|nested] 6+ messages in thread
* 答复: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
2019-08-01 9:20 ` Richard Weinberger
@ 2019-08-01 9:26 ` chengzhihao
2019-08-01 9:40 ` Richard Weinberger
0 siblings, 1 reply; 6+ messages in thread
From: chengzhihao @ 2019-08-01 9:26 UTC (permalink / raw)
To: Richard Weinberger; +Cc: zhangyi (F), linux-mtd, linux-kernel
> You send this patch three times, I guess your mail setup has issues? :-)
Sorry, I thought I hadn't sent the first two e-mails. (The Patch work website refreshes slowly)
> Do you have numbers how many attempts were needed to get a free block?
I tested it dozens of times. The biggest number of attempts I've ever had so far is 6. In most cases, it only takes 2 or 3 times.
-----邮件原件-----
发件人: Richard Weinberger [mailto:richard@nod.at]
发送时间: 2019年8月1日 17:21
收件人: chengzhihao <chengzhihao1@huawei.com>
抄送: zhangyi (F) <yi.zhang@huawei.com>; linux-mtd <linux-mtd@lists.infradead.org>; linux-kernel <linux-kernel@vger.kernel.org>
主题: Re: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
----- Ursprüngliche Mail -----
> Von: "chengzhihao1" <chengzhihao1@huawei.com>
> An: "richard" <richard@nod.at>, "yi zhang" <yi.zhang@huawei.com>
> CC: "linux-mtd" <linux-mtd@lists.infradead.org>, "linux-kernel"
> <linux-kernel@vger.kernel.org>
> Gesendet: Donnerstag, 1. August 2019 11:13:20
> Betreff: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number
> of attempts with polling while getting PEB
> I don't quite understand why a limited number of attempts have been
> made to get a free PEB in ubi_wl_get_peb (in fastmap-wl.c). I proposed
> this PATCH with reference to the implementation of ubi_wl_get_peb (in
> wl.c). As far as I know, getting PEB by polling probably won't fall into soft-lockup.
> ubi_update_fastmap may add new tasks (including erase task or wl
> taskk, wl tasks generally do not generate additional free PEBs) to
> ubi->works, and produce_free_peb will eventually complete all tasks in
> ubi->works or obtain an free PEB that can be filled into pool.
You send this patch three times, I guess your mail setup has issues? :-)
This is one of the darkest corners of Fastmap where things get messy.
The number of retry attempts was limited to avoid a live lock.
I agree that allowing only one retry is a little to few.
With nandsim, a small nand and a fast PC you can hit that.
Do you have numbers how many attempts were needed to get a free block?
Thanks,
//richard
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: 答复: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
2019-08-01 9:26 ` 答复: " chengzhihao
@ 2019-08-01 9:40 ` Richard Weinberger
2019-08-01 13:19 ` 答复: " chengzhihao
0 siblings, 1 reply; 6+ messages in thread
From: Richard Weinberger @ 2019-08-01 9:40 UTC (permalink / raw)
To: chengzhihao1; +Cc: yi zhang, linux-mtd, linux-kernel
----- Ursprüngliche Mail -----
>> Do you have numbers how many attempts were needed to get a free block?
> I tested it dozens of times. The biggest number of attempts I've ever had so far
> is 6. In most cases, it only takes 2 or 3 times.
So raising the retry count to, let's say, 10 would work too?
Having it unbound feels dangerous because it may hide other problems.
Thanks,
//richard
^ permalink raw reply [flat|nested] 6+ messages in thread
* 答复: 答复: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
2019-08-01 9:40 ` Richard Weinberger
@ 2019-08-01 13:19 ` chengzhihao
0 siblings, 0 replies; 6+ messages in thread
From: chengzhihao @ 2019-08-01 13:19 UTC (permalink / raw)
To: Richard Weinberger; +Cc: zhangyi (F), linux-mtd, linux-kernel
I have tested this extreme case(No free PEBs left after creating test volumes) on different type of machines for 100 times. The biggest number of attempts are shown below:
x86_64 arm64
2-core 4 4
4-core 8 4
8-core 4 4
So, setting the number of attempts to 10 is fine. May I send another PATCH to improve it?
Planned revisions:
--- a/drivers/mtd/ubi/fastmap-wl.c
+++ b/drivers/mtd/ubi/fastmap-wl.c
@@ -221,12 +221,12 @@ int ubi_wl_get_peb(struct ubi_device *ubi)
if (pool->used == pool->size) {
spin_unlock(&ubi->wl_lock);
- if (retried) {
+ retried++;
+ if (retried == 10) {
ubi_err(ubi, "Unable to get a free PEB from user WL pool");
ret = -ENOSPC;
goto out;
}
- retried = 1;
up_read(&ubi->fm_eba_sem);
ret = produce_free_peb(ubi);
if (ret < 0) {
-----邮件原件-----
发件人: Richard Weinberger [mailto:richard@nod.at]
发送时间: 2019年8月1日 17:40
收件人: chengzhihao <chengzhihao1@huawei.com>
抄送: zhangyi (F) <yi.zhang@huawei.com>; linux-mtd <linux-mtd@lists.infradead.org>; linux-kernel <linux-kernel@vger.kernel.org>
主题: Re: 答复: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
----- Ursprüngliche Mail -----
>> Do you have numbers how many attempts were needed to get a free block?
> I tested it dozens of times. The biggest number of attempts I've ever
> had so far is 6. In most cases, it only takes 2 or 3 times.
So raising the retry count to, let's say, 10 would work too?
Having it unbound feels dangerous because it may hide other problems.
Thanks,
//richard
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-08-01 13:19 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2019-08-01 9:17 [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB Zhihao Cheng
2019-08-01 9:13 ` 答复: " chengzhihao
2019-08-01 9:20 ` Richard Weinberger
2019-08-01 9:26 ` 答复: " chengzhihao
2019-08-01 9:40 ` Richard Weinberger
2019-08-01 13:19 ` 答复: " chengzhihao
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