On Wed, 2013-12-11 at 17:49 +0000, Al Viro wrote: > On Wed, Dec 11, 2013 at 05:04:41PM +0000, Tvrtko Ursulin wrote: > > Hi all, > > > > It seems that the buffer allocation in seq_read can double in size > > indefinitely, at least I've seen that in practice with /proc/<pid>/smaps > > (attempting to double m->size to 4M on a read of 1000 bytes). This > > produces an ugly WARN_ON_ONCE, which should perhaps be avoided? (given > > that it can be triggered by userspace at will) > > An entry in /proc/<pid>/smaps that did not fit into 2Mb? Seriously? > How in hell has that happened? If you can trigger that at will, please > post the reproducer. Yeah, no, wrong assumption. It was not about the size but the number of reads. For example: open("/proc/3131/smaps", O_RDONLY|O_LARGEFILE) = 3 fstat64(1, {st_mode=S_IFCHR|0666, st_rdev=makedev(1, 3), ...}) = 0 brk(0xf9019000) = 0xf9019000 read(3, "be483000-be4ab000 rw-s 00000000 "..., 4096) = 4054 write(1, "be483000-be4ab000 rw-s 00000000 "..., 4054) = 4054 read(3, "be5c3000-be5c5000 rw-s 10da3f000"..., 4096) = 3656 write(1, "be5c3000-be5c5000 rw-s 10da3f000"..., 3656) = 3656 read(3, "be6b1000-be6b2000 rw-s 10da48000"..., 4096) = 3661 write(1, "be6b1000-be6b2000 rw-s 10da48000"..., 3661) = 3661 read(3, "be6b9000-be6ba000 rw-s 10da38000"..., 4096) = 3599 write(1, "be6b9000-be6ba000 rw-s 10da38000"..., 3599) = 3599 read(3, "be6d6000-be7b6000 rw-s 10d889000"..., 4096) = 3599 write(1, "be6d6000-be7b6000 rw-s 10d889000"..., 3599) = 3599 read(3, "be884000-be885000 rw-s 10d85c000"..., 4096) = 3661 write(1, "be884000-be885000 rw-s 10d85c000"..., 3661) = 3661 read(3, "be88d000-be8de000 rw-p 00000000 "..., 4096) = 4007 write(1, "be88d000-be8de000 rw-p 00000000 "..., 4007) = 4007 read(3, "bea29000-bea4d000 r-xp 00000000 "..., 4096) = 4057 write(1, "bea29000-bea4d000 r-xp 00000000 "..., 4057) = 4057 read(3, "beab3000-bead0000 r--p 00000000 "..., 4096) = 2092 write(1, "beab3000-bead0000 r--p 00000000 "..., 2092) = 2092 read(3, 0xf9017030, 4096) = -1 ENOMEM (Out of memory) Regards, Tvrtko -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html