Re: [syzbot] [kernel?] WARNING in c_start (2)
From: Tetsuo Handa
Date: Sat Mar 11 2023 - 21:58:17 EST
Hello, Linus.
syzbot is unable to test kernels due to hitting WARN_ON_ONCE(cpu >= bits) upon
"cat /proc/cpuinfo" request.
Since commit 596ff4a09b898179 ("cpumask: re-introduce constant-sized cpumask optimizations")
changed to pass "small_cpumask_bits" instead of "nr_cpumask_bits" to find_next_bit(),
find_next_bit() returning small_cpumask_bits causes c_next() to go beyond nr_cpumask_bits.
I think that we need to make sure that cpumask_next() and friends would not return cpu id
beyond nr_cpumask_bits.
Before commit 596ff4a09b898179:
----------
diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 099b6f0d96bd..d2e49c74284a 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -152,10 +152,11 @@ static int show_cpuinfo(struct seq_file *m, void *v)
}
static void *c_start(struct seq_file *m, loff_t *pos)
{
*pos = cpumask_next(*pos - 1, cpu_online_mask);
+ pr_info("*pos = %u, nr_cpu_ids = %u\n", *pos, nr_cpu_ids);
if ((*pos) < nr_cpu_ids)
return &cpu_data(*pos);
return NULL;
}
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 10c92bd9b807..3d7127ebeb44 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -172,10 +172,11 @@ static inline unsigned int cpumask_last(const struct cpumask *srcp)
* Returns >= nr_cpu_ids if no further cpus set.
*/
static inline
unsigned int cpumask_next(int n, const struct cpumask *srcp)
{
+ pr_info("bits = 0x%016lx, nr_cpumask_bits = %u, n + 1 = %u\n", *cpumask_bits(srcp), nr_cpumask_bits, n + 1);
/* -1 is a legal arg here. */
if (n != -1)
cpumask_check(n);
return find_next_bit(cpumask_bits(srcp), nr_cpumask_bits, n + 1);
}
----------
----------
[ 11.626748] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 0
[ 11.626751] *pos = 0, nr_cpu_ids = 10
[ 11.626765] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 1
[ 11.626766] *pos = 1, nr_cpu_ids = 10
[ 11.626775] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 2
[ 11.626775] *pos = 2, nr_cpu_ids = 10
[ 11.626783] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 3
[ 11.626783] *pos = 3, nr_cpu_ids = 10
[ 11.626791] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 4
[ 11.626791] *pos = 4, nr_cpu_ids = 10
[ 11.626819] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 4
[ 11.626820] *pos = 4, nr_cpu_ids = 10
[ 11.626828] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 5
[ 11.626828] *pos = 5, nr_cpu_ids = 10
[ 11.626835] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 6
[ 11.626836] *pos = 6, nr_cpu_ids = 10
[ 11.626843] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 7
[ 11.626844] *pos = 7, nr_cpu_ids = 10
[ 11.626851] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 8
[ 11.626851] *pos = 8, nr_cpu_ids = 10
[ 11.626862] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 8
[ 11.626863] *pos = 8, nr_cpu_ids = 10
[ 11.626870] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 9
[ 11.626871] *pos = 9, nr_cpu_ids = 10
[ 11.626878] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 10
[ 11.626879] *pos = 10, nr_cpu_ids = 10
[ 11.626883] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 10
[ 11.626884] *pos = 10, nr_cpu_ids = 10
[ 11.639390] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 0
[ 11.639392] *pos = 0, nr_cpu_ids = 10
[ 11.639406] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 1
[ 11.639407] *pos = 1, nr_cpu_ids = 10
[ 11.639416] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 2
[ 11.639417] *pos = 2, nr_cpu_ids = 10
[ 11.639424] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 3
[ 11.639425] *pos = 3, nr_cpu_ids = 10
[ 11.639432] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 4
[ 11.639433] *pos = 4, nr_cpu_ids = 10
[ 11.639459] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 4
[ 11.639459] *pos = 4, nr_cpu_ids = 10
[ 11.639467] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 5
[ 11.639467] *pos = 5, nr_cpu_ids = 10
[ 11.639475] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 6
[ 11.639475] *pos = 6, nr_cpu_ids = 10
[ 11.639483] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 7
[ 11.639483] *pos = 7, nr_cpu_ids = 10
[ 11.639490] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 8
[ 11.639491] *pos = 8, nr_cpu_ids = 10
[ 11.639503] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 8
[ 11.639503] *pos = 8, nr_cpu_ids = 10
[ 11.639510] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 9
[ 11.639511] *pos = 9, nr_cpu_ids = 10
[ 11.639518] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 10
[ 11.639519] *pos = 10, nr_cpu_ids = 10
[ 11.639524] bits = 0x00000000000003ff, nr_cpumask_bits = 10, n + 1 = 10
[ 11.639524] *pos = 10, nr_cpu_ids = 10
----------
After commit 596ff4a09b898179:
----------
diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 099b6f0d96bd..d2e49c74284a 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -152,10 +152,11 @@ static int show_cpuinfo(struct seq_file *m, void *v)
}
static void *c_start(struct seq_file *m, loff_t *pos)
{
*pos = cpumask_next(*pos - 1, cpu_online_mask);
+ pr_info("*pos = %u, nr_cpu_ids = %u\n", *pos, nr_cpu_ids);
if ((*pos) < nr_cpu_ids)
return &cpu_data(*pos);
return NULL;
}
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 8fbe76607965..0aaa0a32a39f 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -205,10 +205,11 @@ static inline unsigned int cpumask_last(const struct cpumask *srcp)
* Returns >= nr_cpu_ids if no further cpus set.
*/
static inline
unsigned int cpumask_next(int n, const struct cpumask *srcp)
{
+ pr_info("bits = 0x%016lx, small_cpumask_bits = %u, n + 1 = %u\n", *cpumask_bits(srcp), small_cpumask_bits, n + 1);
/* -1 is a legal arg here. */
if (n != -1)
cpumask_check(n);
return find_next_bit(cpumask_bits(srcp), small_cpumask_bits, n + 1);
}
----------
----------
[ 10.954521] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 0
[ 10.954525] *pos = 0, nr_cpu_ids = 10
[ 10.954544] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 1
[ 10.954545] *pos = 1, nr_cpu_ids = 10
[ 10.954557] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 2
[ 10.954557] *pos = 2, nr_cpu_ids = 10
[ 10.954568] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 3
[ 10.954569] *pos = 3, nr_cpu_ids = 10
[ 10.954580] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 4
[ 10.954580] *pos = 4, nr_cpu_ids = 10
[ 10.954625] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 4
[ 10.954627] *pos = 4, nr_cpu_ids = 10
[ 10.954638] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 5
[ 10.954638] *pos = 5, nr_cpu_ids = 10
[ 10.954649] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 6
[ 10.954649] *pos = 6, nr_cpu_ids = 10
[ 10.954660] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 7
[ 10.954660] *pos = 7, nr_cpu_ids = 10
[ 10.954671] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 8
[ 10.954671] *pos = 8, nr_cpu_ids = 10
[ 10.954689] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 8
[ 10.954689] *pos = 8, nr_cpu_ids = 10
[ 10.954700] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 9
[ 10.954701] *pos = 9, nr_cpu_ids = 10
[ 10.954711] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 10
[ 10.954712] *pos = 64, nr_cpu_ids = 10
[ 10.954720] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 64
[ 10.954830] ------------[ cut here ]------------
[ 10.954832] WARNING: CPU: 0 PID: 417 at include/linux/cpumask.h:143 c_start+0xb4/0xe0
[ 10.954838] Modules linked in: sch_fq_codel(E) msr(E) ip_tables(E) x_tables(E) autofs4(E) btrfs(E) raid10(E) raid456(E) async_raid6_recov(E) async_memcpy(E) async_pq(E) async_xor(E) async_tx(E) raid6_pq(E) xor(E) libcrc32c(E) raid1(E) raid0(E) multipath(E) linear(E) crct10dif_pclmul(E) crc32_pclmul(E) ghash_clmulni_intel(E) aesni_intel(E) crypto_simd(E) ahci(E) cryptd(E) psmouse(E) libahci(E) e1000(E) i2c_piix4(E) pata_acpi(E)
[ 10.954862] CPU: 0 PID: 417 Comm: grep Tainted: G E 6.2.0+ #950
[ 10.954865] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[ 10.954866] RIP: 0010:c_start+0xb4/0xe0
[ 10.954868] Code: 82 e9 01 48 39 c3 7d 17 48 83 fb 40 73 2a 48 c7 c0 a0 98 01 00 48 03 04 dd e0 c9 c7 a6 eb 02 31 c0 48 83 c4 08 5b 41 5e 5d c3 <0f> 0b 83 fb 3f 76 8e be 40 00 00 00 eb ad 48 c7 c7 10 59 24 a7 48
[ 10.954870] RSP: 0018:ffff9d5d80943d58 EFLAGS: 00010293
[ 10.954872] RAX: 000000000000003f RBX: 0000000000000040 RCX: e79682b5424b6f00
[ 10.954874] RDX: 0000000000001fff RSI: 0000000000000000 RDI: ffff8eb1db821608
[ 10.954877] RBP: ffff9d5d80943d70 R08: 3436203d2031202b R09: 206e202c3436203d
[ 10.954878] R10: 203d20737469625f R11: 6b73616d7570635f R12: ffff8eb1c764e650
[ 10.954879] R13: ffff9d5d80943e20 R14: ffff8eb1c764e640 R15: 0000000000000000
[ 10.954880] FS: 00007ff2c79b7740(0000) GS:ffff8eb1db800000(0000) knlGS:0000000000000000
[ 10.954882] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 10.954884] CR2: 0000559fdf1c6000 CR3: 0000000108b9a004 CR4: 00000000000306f0
[ 10.954887] Call Trace:
[ 10.954888] <TASK>
[ 10.954890] seq_read_iter+0x11c/0x410
[ 10.954895] proc_reg_read_iter+0xe3/0x110
[ 10.954898] vfs_read+0x23c/0x2a0
[ 10.954901] ksys_read+0x6d/0xd0
[ 10.954902] __x64_sys_read+0x1f/0x30
[ 10.954904] do_syscall_64+0x68/0x90
[ 10.954907] ? exc_page_fault+0x92/0x240
[ 10.954909] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 10.954911] RIP: 0033:0x7ff2c7714992
[ 10.954913] Code: c0 e9 b2 fe ff ff 50 48 8d 3d fa b2 0c 00 e8 c5 1d 02 00 0f 1f 44 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24
[ 10.954915] RSP: 002b:00007fff5a069b28 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[ 10.954917] RAX: ffffffffffffffda RBX: 0000000000001000 RCX: 00007ff2c7714992
[ 10.954918] RDX: 0000000000016000 RSI: 0000559fdf1c658a RDI: 0000000000000003
[ 10.954919] RBP: 0000559fdf1c658a R08: 0000000000019000 R09: 0000000000000000
[ 10.954920] R10: 0000000000000066 R11: 0000000000000246 R12: 0000000000000003
[ 10.954921] R13: 0000000000016000 R14: 00007fff5a069be0 R15: 0000000000016000
[ 10.954923] </TASK>
[ 10.954924] ---[ end trace 0000000000000000 ]---
[ 10.954925] *pos = 64, nr_cpu_ids = 10
[ 10.977061] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 0
[ 10.977064] *pos = 0, nr_cpu_ids = 10
[ 10.977079] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 1
[ 10.977080] *pos = 1, nr_cpu_ids = 10
[ 10.977089] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 2
[ 10.977090] *pos = 2, nr_cpu_ids = 10
[ 10.977098] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 3
[ 10.977098] *pos = 3, nr_cpu_ids = 10
[ 10.977106] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 4
[ 10.977107] *pos = 4, nr_cpu_ids = 10
[ 10.977133] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 4
[ 10.977134] *pos = 4, nr_cpu_ids = 10
[ 10.977142] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 5
[ 10.977143] *pos = 5, nr_cpu_ids = 10
[ 10.977150] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 6
[ 10.977151] *pos = 6, nr_cpu_ids = 10
[ 10.977159] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 7
[ 10.977159] *pos = 7, nr_cpu_ids = 10
[ 10.977167] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 8
[ 10.977167] *pos = 8, nr_cpu_ids = 10
[ 10.977179] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 8
[ 10.977180] *pos = 8, nr_cpu_ids = 10
[ 10.977187] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 9
[ 10.977188] *pos = 9, nr_cpu_ids = 10
[ 10.977196] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 10
[ 10.977196] *pos = 64, nr_cpu_ids = 10
[ 10.977201] bits = 0x00000000000003ff, small_cpumask_bits = 64, n + 1 = 64
[ 10.979923] *pos = 64, nr_cpu_ids = 10
----------
On 2023/03/10 9:42, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 44889ba56cbb Merge tag 'net-6.3-rc2' of git://git.kernel.o..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13933824c80000
> kernel config: https://syzkaller.appspot.com/x/.config?x=d677dcd743eef09
> dashboard link: https://syzkaller.appspot.com/bug?extid=96cae094d90877641f32
> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+96cae094d90877641f32@xxxxxxxxxxxxxxxxxxxxxxxxx