[Bug 219476] [i386] 11.1-PRERELEASE double panics due to low kern.kstack_pages default

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=219476

            Bug ID: 219476
           Summary: [i386] 11.1-PRERELEASE double panics due to low
                    kern.kstack_pages default
           Product: Base System
           Version: 11.0-STABLE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: eugen at freebsd.org

stable/11 got lots of kernel level code that abuses small default stack of i386
kernel threads: ZFS, IPSEC, SCTP, device drivers etc. Overflow of kernel stack
produces "double fault" panics.

kern.kstack_pages is loader tunnable now for i386. The system should be stable
out of the box, so we should increase default for kern.kstack_pages. Loader
tunnable can serve users of i386 systems that are unhappy with new default,
they can decrease it with /boot/loader.conf

Some examples:

* sys/netinet/sctp_pcb.c, function sctp_load_addresses_from_init() allocates
2184 bytes on stack (disassemble: sub $0x888,%esp);

* sys/netinet/sctp_auth.c: sctp_auth_get_cookie_params(): 1592 bytes on stack;

* src/sys/contrib/dev/ath/ath_hal/ar9300/ar9300_eeprom.c:
ar9300_eeprom_restore_internal_address(): 2092 bytes on stack;

* sys/contrib/dev/ath/ath_hal/ar9300/ar9300_paprd.c: create_pa_curve(): 1416
bytes;

* sys/libkern/zlib.c: huft_build(): 1420 bytes;

And so on. Here is "top-list" for my home router custom kernel (1GB RAM, no
swap):

Bytes-on-stack  In-module
2184            sctp_pcb.o
2092            ar9300_eeprom.o
2080            kern_linker.o
1664            cryptosoft.o
1592            sctp_auth.o
1536            glxsb_hash.o
1420            zlib.o
1416            ar9300_paprd.o
1352            scsi_da.o
1344            nfs_nfsdport.o
1328            vm_object.o
1312            fortuna.o
1232            cam_periph.o
1224            zlib.o
1192            cam_xpt.o
1192            ata_da.o
1184            cam_xpt.o
1168            ata_da.o
1160            sctp_output.o

Some of "network hot path" subroutines not shown here do abuse kernel stack
too, for example SHA256_Transform() from sys/crypto/sha2/sha256c.c that may be
actively used with IPSEC processing.

ae@'s https://reviews.freebsd.org/D10869 deals with IPSEC in part and helps in
my case, at least while there is no ZFS involved. However, it is impossible to
perform similar cleanup for each and every kernel subsystem in near future and
double panics with current defaults are bad too.

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