rust: alloc: implement `try_format!` macro #478

jablonskim · 2021-08-03T19:13:07Z

Implement try_format! macro - an equivalent of format! that will never panic on memory allocation failure. It returns an error instead.

The try_format! macro uses a StringWriter helper internally that implements Write trait for a String in a way that never panics during memory allocation.

The usage of try_format! is demonstrated in the rust_minimal sample module.

Based on #476.

This commit adds the following methods to `String` structure: - `try_with_capacity` - `try_push_str` - `try_shrink_to_fit` - `try_push` - `try_into_boxed_str` Those are panic-free equivalents of already existing methods. They may be useful for `String` creation inside kernel code. Signed-off-by: Mateusz Jabłoński <[email protected]>

jablonskim · 2021-08-03T19:23:05Z

rust/alloc/string.rs

+/// ```
+#[stable(feature = "kernel", since = "1.0.0")]
+#[derive(Debug)]
+pub struct StringWriter {


Personally, I do not like the name StringWriter. The information about the panic-free logic ant it's purpose is missing, but I had no better idea for the name to be descriptive but also short and clean. If you have any ideas for a better name, feel free to comment.

This shouldn't be pub.

I have made it public because it seemed to me that it may be useful in some other places too. For example, one may use it like that:

let mut sw = StringWriter::try_with_capacity(0)?; write!(&mut sw, "test {}\n", 1).unwrap(); write!(&mut sw, "test {}\n", 2).unwrap(); let s = sw.into_string()?;

What do you think?

rust/alloc/macros.rs

rust/alloc/string.rs

The `StringWriter` type is a helper type, that implements `Write` trait for a `String` type in a way that never panics during memory allocation. Instead, if any memory allocation during all writing and formatting operations executed on the `StringWriter` fail, it saves the error and returns it as a result when the result of the writing and formatting is requested. Signed-off-by: Mateusz Jabłoński <[email protected]>

Implement `try_format!` macro - an equivalent of `format!` that will never panic on memory allocation failure. It returns an error instead. Signed-off-by: Mateusz Jabłoński <[email protected]>

Signed-off-by: Mateusz Jabłoński <[email protected]>

Shuang reported that the following script: 1) tc qdisc add dev ddd0 handle 10: parent 1: ets bands 8 strict 4 priomap 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 2) mausezahn ddd0 -A 10.10.10.1 -B 10.10.10.2 -c 0 -a own -b 00:c1:a0:c1:a0:00 -t udp & 3) tc qdisc change dev ddd0 handle 10: ets bands 4 strict 2 quanta 2500 2500 priomap 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 crashes systematically when line 2) is commented: list_del corruption, ffff8e028404bd30->next is LIST_POISON1 (dead000000000100) ------------[ cut here ]------------ kernel BUG at lib/list_debug.c:47! invalid opcode: 0000 [#1] PREEMPT SMP NOPTI CPU: 0 PID: 954 Comm: tc Not tainted 5.16.0-rc4+ #478 Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014 RIP: 0010:__list_del_entry_valid.cold.1+0x12/0x47 Code: fe ff 0f 0b 48 89 c1 4c 89 c6 48 c7 c7 08 42 1b 87 e8 1d c5 fe ff 0f 0b 48 89 fe 48 89 c2 48 c7 c7 98 42 1b 87 e8 09 c5 fe ff <0f> 0b 48 c7 c7 48 43 1b 87 e8 fb c4 fe ff 0f 0b 48 89 f2 48 89 fe RSP: 0018:ffffae46807a3888 EFLAGS: 00010246 RAX: 000000000000004e RBX: 0000000000000007 RCX: 0000000000000202 RDX: 0000000000000000 RSI: ffffffff871ac536 RDI: 00000000ffffffff RBP: ffffae46807a3a10 R08: 0000000000000000 R09: c0000000ffff7fff R10: 0000000000000001 R11: ffffae46807a36a8 R12: ffff8e028404b800 R13: ffff8e028404bd30 R14: dead000000000100 R15: ffff8e02fafa2400 FS: 00007efdc92e4480(0000) GS:ffff8e02fb600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000682f48 CR3: 00000001058be000 CR4: 0000000000350ef0 Call Trace: <TASK> ets_qdisc_change+0x58b/0xa70 [sch_ets] tc_modify_qdisc+0x323/0x880 rtnetlink_rcv_msg+0x169/0x4a0 netlink_rcv_skb+0x50/0x100 netlink_unicast+0x1a5/0x280 netlink_sendmsg+0x257/0x4d0 sock_sendmsg+0x5b/0x60 ____sys_sendmsg+0x1f2/0x260 ___sys_sendmsg+0x7c/0xc0 __sys_sendmsg+0x57/0xa0 do_syscall_64+0x3a/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7efdc8031338 Code: 89 02 48 c7 c0 ff ff ff ff eb b5 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 8d 05 25 43 2c 00 8b 00 85 c0 75 17 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 41 54 41 89 d4 55 RSP: 002b:00007ffdf1ce9828 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 0000000061b37a97 RCX: 00007efdc8031338 RDX: 0000000000000000 RSI: 00007ffdf1ce9890 RDI: 0000000000000003 RBP: 0000000000000000 R08: 0000000000000001 R09: 000000000078a940 R10: 000000000000000c R11: 0000000000000246 R12: 0000000000000001 R13: 0000000000688880 R14: 0000000000000000 R15: 0000000000000000 </TASK> Modules linked in: sch_ets sch_tbf dummy rfkill iTCO_wdt iTCO_vendor_support intel_rapl_msr intel_rapl_common joydev pcspkr i2c_i801 virtio_balloon i2c_smbus lpc_ich ip_tables xfs libcrc32c crct10dif_pclmul crc32_pclmul crc32c_intel serio_raw ghash_clmulni_intel ahci libahci libata virtio_blk virtio_console virtio_net net_failover failover sunrpc dm_mirror dm_region_hash dm_log dm_mod [last unloaded: sch_ets] ---[ end trace f35878d1912655c2 ]--- RIP: 0010:__list_del_entry_valid.cold.1+0x12/0x47 Code: fe ff 0f 0b 48 89 c1 4c 89 c6 48 c7 c7 08 42 1b 87 e8 1d c5 fe ff 0f 0b 48 89 fe 48 89 c2 48 c7 c7 98 42 1b 87 e8 09 c5 fe ff <0f> 0b 48 c7 c7 48 43 1b 87 e8 fb c4 fe ff 0f 0b 48 89 f2 48 89 fe RSP: 0018:ffffae46807a3888 EFLAGS: 00010246 RAX: 000000000000004e RBX: 0000000000000007 RCX: 0000000000000202 RDX: 0000000000000000 RSI: ffffffff871ac536 RDI: 00000000ffffffff RBP: ffffae46807a3a10 R08: 0000000000000000 R09: c0000000ffff7fff R10: 0000000000000001 R11: ffffae46807a36a8 R12: ffff8e028404b800 R13: ffff8e028404bd30 R14: dead000000000100 R15: ffff8e02fafa2400 FS: 00007efdc92e4480(0000) GS:ffff8e02fb600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000682f48 CR3: 00000001058be000 CR4: 0000000000350ef0 Kernel panic - not syncing: Fatal exception in interrupt Kernel Offset: 0x4e00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff) ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]--- we can remove 'q->classes[i].alist' only if DRR class 'i' was part of the active list. In the ETS scheduler DRR classes belong to that list only if the queue length is greater than zero: we need to test for non-zero value of 'q->classes[i].qdisc->q.qlen' before removing from the list, similarly to what has been done elsewhere in the ETS code. Fixes: de6d259 ("net/sched: sch_ets: don't peek at classes beyond 'nbands'") Reported-by: Shuang Li <[email protected]> Signed-off-by: Davide Caratti <[email protected]> Signed-off-by: David S. Miller <[email protected]>

jablonskim commented Aug 3, 2021

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bjorn3 reviewed Aug 3, 2021

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bjorn3 reviewed Aug 3, 2021

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jablonskim added 3 commits August 7, 2021 13:10

rust: alloc: add try_format! macro

6cc6f2f

Implement `try_format!` macro - an equivalent of `format!` that will never panic on memory allocation failure. It returns an error instead. Signed-off-by: Mateusz Jabłoński <[email protected]>

rust: samples: use try_format! in sample module

b53aa8d

Signed-off-by: Mateusz Jabłoński <[email protected]>

jablonskim force-pushed the try-format branch from 604f25a to b53aa8d Compare August 7, 2021 13:16

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rust: alloc: implement `try_format!` macro #478

rust: alloc: implement `try_format!` macro #478

jablonskim commented Aug 3, 2021 •

edited

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jablonskim Aug 3, 2021

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jablonskim Aug 8, 2021

rust: alloc: implement try_format! macro #478

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rust: alloc: implement try_format! macro #478

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rust: alloc: implement `try_format!` macro #478

rust: alloc: implement `try_format!` macro #478

jablonskim commented Aug 3, 2021 •

edited

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