答复: 答复: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
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-core4 4
4-core8 4
8-core4 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(>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(>fm_eba_sem);
ret = produce_free_peb(ubi);
if (ret < 0) {
-邮件原件-
发件人: Richard Weinberger [mailto:rich...@nod.at]
发送时间: 2019年8月1日 17:40
收件人: chengzhihao
抄送: zhangyi (F) ; linux-mtd
; linux-kernel
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
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
答复: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
> 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:rich...@nod.at] 发送时间: 2019年8月1日 17:21 收件人: chengzhihao 抄送: zhangyi (F) ; linux-mtd ; linux-kernel 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" > An: "richard" , "yi zhang" > CC: "linux-mtd" , "linux-kernel" > > 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
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" > An: "richard" , "yi zhang" > CC: "linux-mtd" , "linux-kernel" > > 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
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.
-邮件原件-
发件人: chengzhihao
发送时间: 2019年8月1日 17:18
收件人: rich...@nod.at; zhangyi (F)
抄送: linux-...@lists.infradead.org; linux-kernel@vger.kernel.org; chengzhihao
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-rc2-1-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
---
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 = >fm_pool;
struct ubi_fm_pool *wl_pool = >fm_wl_pool;
@@ -220,13 +220,14 @@ int ubi_wl_get_peb(struct ubi_device *ubi)
}
if (pool->used == pool->size) {
- spin_unlock(>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(>works));
+ spin_unlock(>wl_lock);
ret = -ENOSPC;
goto out;
}
- retried = 1;
+ spin_unlock(>wl_lock);
up_read(>fm_eba_sem);
ret = produce_free_peb(ubi);
if (ret < 0) {
--
2.7.4
[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-rc2-1-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
---
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 = >fm_pool;
struct ubi_fm_pool *wl_pool = >fm_wl_pool;
@@ -220,13 +220,14 @@ int ubi_wl_get_peb(struct ubi_device *ubi)
}
if (pool->used == pool->size) {
- spin_unlock(>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(>works));
+ spin_unlock(>wl_lock);
ret = -ENOSPC;
goto out;
}
- retried = 1;
+ spin_unlock(>wl_lock);
up_read(>fm_eba_sem);
ret = produce_free_peb(ubi);
if (ret < 0) {
--
2.7.4
