Messages in this thread | | | Subject | Re: [PATCH] mtd_blkdevs: add mtd_table_mutex lock back to blktrans_{open, release} to avoid race condition | From | Liwei Song <> | Date | Mon, 5 Sep 2022 16:15:46 +0800 |
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On 8/10/22 15:47, Liwei Song wrote: > > > On 8/9/22 17:03, Liwei Song wrote: >> >> >> On 8/9/22 16:08, ChristophHellwig wrote: >>> On Tue, Aug 09, 2022 at 03:57:53PM +0800, Liwei Song wrote: >>>> without lock mtd_table_mutex in blktrans_{open, release}, there will >>>> be a race condition when access devices /dev/mtd1 and /dev/mtdblock1 >>>> at the same time with a high frequency open and close test: >>>> >>>> kernel BUG at drivers/mtd/mtdcore.c:1221! >>>> lr : blktrans_release+0xb0/0x120 >>> >>> This does not seem on a current mainline kernel and seems to be >>> a somewhat incomplete backtrace. Can you send the full dmesg of >>> a latest mainline run and maybe share the reproducer? >> >> Yes, the kernel I used is 5.15, unfortunately this is the latest version >> that worked on my board, the whole log is: >> >> [ 31.301343] ------------[ cut here ]------------ >> [ 31.301343] ------------[ cut here ]------------ >> [ 31.301365] kernel BUG at drivers/mtd/mtdcore.c:1221! >> [ 31.314981] kernel BUG at drivers/mtd/mtdcore.c:1221! >> [ 31.329328] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP >> [ 31.374117] Modules linked in: 8021q sch_fq_codel openvswitch nsh nf_conncount nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 fuse >> [ 31.395820] CPU: 2 PID: 390 Comm: a.out Not tainted 5.15.58-yocto-standard #1 >> [ 31.412672] Hardware name: SoCFPGA Agilex SoCDK (DT) >> [ 31.427372] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) >> [ 31.444058] pc : __put_mtd_device+0x4c/0x84 >> [ 31.457977] lr : put_mtd_device+0x3c/0x5c >> [ 31.464122] sp : ffff80000c26bc50 >> [ 31.466126] x29: ffff80000c26bc50 x28: ffff000285785100 x27: 0000000000000000 >> [ 31.471945] x26: 0000000045585401 x25: 0000000000000000 x24: ffff000285785768 >> [ 31.477762] x23: ffff0002803ee520 x22: ffff0002804f8900 x21: ffff000281956800 >> [ 31.483580] x20: ffff000281956800 x19: ffff000281955080 x18: 0000000000000000 >> [ 31.489402] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 >> [ 31.495219] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 >> [ 31.501037] x11: 0000000000000000 x10: 0000000000000000 x9 : ffff8000088a79b0 >> [ 31.506855] x8 : ffff80000c26bcb0 x7 : 0000000000000000 x6 : 0000000000000001 >> [ 31.512673] x5 : ffff000280959488 x4 : 0000000000000000 x3 : 0000000000000000 >> [ 31.518491] x2 : ffff000281956800 x1 : 00000000ffffffff x0 : ffff000281955080 >> [ 31.524310] Call trace: >> [ 31.525450] __put_mtd_device+0x4c/0x84 >> [ 31.527979] put_mtd_device+0x3c/0x5c >> [ 31.530333] mtdchar_close+0x3c/0x84 >> [ 31.532604] __fput+0x78/0x220 >> [ 31.534357] ____fput+0x1c/0x30 >> [ 31.536193] task_work_run+0x88/0xc0 >> [ 31.538467] do_notify_resume+0x384/0x12a0 >> [ 31.541261] el0_svc+0x6c/0x80 >> [ 31.543015] el0t_64_sync_handler+0xa4/0x130 >> [ 31.545977] el0t_64_sync+0x1a0/0x1a4 >> [ 31.548338] Code: b9448841 51000421 b9048841 36ffff41 (d4210000) >> [ 31.553115] ---[ end trace 9652b26ea1d7daa1 ]--- >> [ 31.556420] Internal error: Oops - BUG: 0 [#2] PREEMPT SMP >> [ 31.556420] note: a.out[390] exited with preempt_count 1 >> [ 31.560588] Modules linked in: 8021q sch_fq_codel openvswitch nsh nf_conncount nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 fuse >> [ 31.575265] CPU: 3 PID: 391 Comm: a.out Tainted: G D 5.15.58-yocto-standard #1 >> [ 31.582466] Hardware name: SoCFPGA Agilex SoCDK (DT) >> [ 31.586115] pstate: 40000005 (nZcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) >> [ 31.591757] pc : __put_mtd_device+0x4c/0x84 >> [ 31.594642] lr : blktrans_release+0xb0/0x120 >> [ 31.597603] sp : ffff80000c22bc20 >> [ 31.599608] x29: ffff80000c22bc20 x28: ffff000285785e80 x27: 0000000000000000 >> [ 31.605428] x26: 0000000045585401 x25: 0000000000000000 x24: ffff0002857864e8 >> [ 31.611247] x23: ffff0002803ee520 x22: ffff0002803e3470 x21: ffff0002803e3400 >> [ 31.617066] x20: ffff0002803e3020 x19: ffff000281955080 x18: 0000000000000000 >> [ 31.622884] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 >> [ 31.628702] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 >> [ 31.634519] x11: 0000000000000000 x10: 0000000000000000 x9 : ffff8000088b0230 >> [ 31.640337] x8 : ffff80000c22bb90 x7 : 0000000000000000 x6 : 0000000000000001 >> [ 31.646155] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000 >> [ 31.651973] x2 : ffff000281956800 x1 : 00000000ffffffff x0 : ffff000281955080 >> [ 31.657792] Call trace: >> [ 31.658933] __put_mtd_device+0x4c/0x84 >> [ 31.661462] blktrans_release+0xb0/0x120 >> [ 31.664077] blkdev_put+0xd4/0x210 >> [ 31.666175] blkdev_close+0x34/0x50 >> [ 31.668355] __fput+0x78/0x220 >> [ 31.670108] ____fput+0x1c/0x30 >> [ 31.671943] task_work_run+0x88/0xc0 >> [ 31.674217] do_notify_resume+0x384/0x12a0 >> [ 31.677009] el0_svc+0x6c/0x80 >> [ 31.678762] el0t_64_sync_handler+0xa4/0x130 >> [ 31.681723] el0t_64_sync+0x1a0/0x1a4 >> [ 31.684082] Code: b9448841 51000421 b9048841 36ffff41 (d4210000) >> [ 31.688857] ---[ end trace 9652b26ea1d7daa2 ]--- >> [ 31.692161] note: a.out[391] exited with preempt_count 1 >> >> the testcase a.out is compiled from below code: >> when run the case /dev/mtd1 and /dev/mtdblock1 will be used for open and close test. >> >> #include <stdio.h> >> #include <stdlib.h> >> #include <sys/types.h> >> #include <sys/stat.h> >> #include <fcntl.h> >> #include <string.h> >> #include <signal.h> >> #include <unistd.h> >> >> int main(int argc, char *argv[]) >> { >> pid_t pid, pid1, pid2; >> int fd,ret = 0; >> int status = 0; >> char device_char[12]="/dev/mtd"; >> char device_block[17]="/dev/mtdblock"; >> >> strcat(device_char, argv[1]); >> strcat(device_block, argv[1]); >> >> pid1 = fork(); >> if(pid1 == 0){ >> while(1){ >> fd = open(device_char, O_SYNC|O_RDWR); >> ret = close(fd); >> } >> } >> pid2 = fork(); >> if(pid2 == 0){ >> while(1){ >> fd = open(device_block, O_SYNC|O_RDWR); >> ret = close(fd); >> } >> } >> sleep(10); >> kill(pid1, SIGKILL); >> kill(pid2, SIGKILL); >> pid = wait(&status); >> pid = wait(&status); >> return 0; >> } >> >>> >>>> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c >>>> index b8ae1ec14e17..147e4a11dfe4 100644 >>>> --- a/drivers/mtd/mtd_blkdevs.c >>>> +++ b/drivers/mtd/mtd_blkdevs.c >>>> @@ -188,6 +188,8 @@ static int blktrans_open(struct block_device *bdev, fmode_t mode) >>>> >>>> kref_get(&dev->ref); >>>> >>>> + if (!mutex_trylock(&mtd_table_mutex)) >>>> + return ret; >>> >>> No, that's not really the solution. >>> >>> Turning the kref_get above into a kref_get_unless_zero might be better >>> path to look into. >> >> Thanks, I will have a look at this. > > Hi Christoph, > > It seems this way can not stop the race to decrease/increase mtd->usecount, > the race condition is between mtdchar_{open, close}()->(get)put_mtd_device()->__(get)put_mtd_device() > and blktrans_{open,release}()-> __(get)put_mtd_device(), when operate the same device > as char device(/dev/mtd1) and block device(/dev/mtdblock1), the original fix for > this issue is 073db4a51ee4 ("mtd: fix: avoid race condition when accessing mtd->usecount"), > Could you give some suggestion about this?
Hi,
Any suggestion about my new found?
Thanks, Liwei.
> > Thanks, > Liwei. > > > >> >> Liwei. >> >> >>>
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