Message ID | 0B80F9D4116B2F4484E7279D5A66984F7A8A13@dggemi524-mbx.china.huawei.com |
---|---|
State | Not Applicable |
Headers | show |
Series | 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB | expand |
----- 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
> 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
----- 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
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)
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(-) } 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